It doesn't matter what the Sea Folk Windfinders can or can't do. Before you look at military possibilities, you need to look into HOW Demandred could possibly make the Windfinders turn against the Light that, after the Coramoor launched the LB, they would all of a sudden attack the cities of his allies...

It's simple Shannow. Either Demandred will rely massively on the Shadow's resources (Shadowspawn, Dreadlords and what not, people who know they serve the Shadow)... or he will have secured an army of the Light he could use in a deception, a proxy war.

It's more likely to be both: armies of the Light to start a Light vs. Light war, and armies of the Shadow for other purposes and eventually wipe out the survivors of the proxy war.

This is what Semirhage was working on, having positionned herself near the one who had absolute power over the Seanchan. At any time, and not too soon to risk attracting attention, she could in a blink take full control of Tuon and guide all her actions in the LB.

Just look at what his ally Mesaana has done: place a Red on the Amyrlin Seat, let her antagonize Rand deeply, let her send an expedition to the BT to which Taim, forewarned no doubt, replied by having the Light's faction at the BT bond those sisters. Mesaana used Elaida and key-positionned BA to split the Tower in two factions, which she was on her way to turn into ten factions (the seven Ajahs growing into enemies of each other in the Tower, Rebel BA Sitters having encouraged the division in their Hall into three factions more and more divided). Mesaana has almost succeeded at reducing the AS Rand could use in the LB to a small faction around Cadsuane... Then Semirhage got captured, Moridin tied Mesaana's hands with Egwene and between Egwene's campaign to undermine Elaida and the Seanchan's raid frightening the WT to the core, Mesaana failed spectacularly.

But before that fiasco, Mesaana was another an inch away from being able to take full control of the Amyrlin Seat when the LB start, and turn all the factions of the WT into a proxy war to stop Elaida. None of those factions could work with each other anymore... it bode well.

We know from Sammael one of Demandred's favourite strategies is to get his enemies to fight one another in proxy wars. Not only that keeps them busy from doing something else... like turning to the real enemy, but it means you eventually strike at the victor or the two factions now weakened into a stalemate.

Semirhage was controlling the hugest army on the continent, an army set on conquering all the lands, with irreconciable antagonism toward Rand's channellers.. Windfinders, WO, Aes Sedai, Asha'man.

Mesaana had undermined completely the potential of the WT as Rand's biggest ally. Mesaana had created from the start her own "Latra Posae".

Rand had set the ball rolling to rebuild a male half to the AS guild, but Mazrim Taim not only worked to make it damn hard for the WT/Asha'man to trust one another, but has built himself an army of dreadlords within Rand's group.

Look for Demandred to have accomplished something complementary to what Semirhage and Mesaana were preparing. For the channellers, it's pretty obvious: he's the one who set the ball rolling at the Black Tower. The primary goal was to make it impossible for Rand to unite the BT men and the female channellers. Getting dreadlords was a mere bonus. You'd think if Demandred cared so much to get a lot of Dreadlords, he would have convinced Mesaana not to waste her BA resources... those women could be trained, or used for circles... and he would have set himself up at the BT, not let Taim be the one gaining those serving the Shadow's loyalty...

Relying on channellers isn't Demandred's goal. He doesn't need to build himself an army, he's got billions of Shadowspawn.

He's rather gambled on starting a giant proxy war. It's been a while now we've known the biggest risks hanging over the head of the Light's forces: Rand is convinced he can't face both the Seanchan and the Shadow. Don't you think Demandred has not made the reverse calculation: the Shadow can't face the Seanchan and Rand's half of the Light united? Of course he did. The situation became far worse since at Tar Valon on the eve of TG the situation turned from Mesaana reaching absolute and final success one day to utter and final failure the next day. All Demandred can hope for now with that half of the Light is that he'll get lucky and Egwene and Rand won't manage to reach an agreement and the nations will split between the two leaderships.

If you want to convince me Demandred had any interest in placing himself as the master trader/head of security of the SF, come up with his strategy to turn the Windfinders and SF against the Light, or how he could start a proxy war using them. Waging war on the Westlands is the last thing the Sea Folk would ever do. They don't want to be involved in any way in continental war. They would never seize coastal cities. They want to increase their trade Empire. They have got Travelling, and begun to secure small patches of land, inland. What do you think they're up to? Zaida has seen the advantage of Travelling immediately, the Sea Folk are preparing to offer Gateway-based trade for a price. Part of this is simply commerce, part of this is compensating for the Seanchan's presence in the Sea of Storms which has increased the risks of Sea-based trade and reduced their ports of entry to their markets... Elayne has figured it out, she's secured her own deal with the Kin to free Andor-Cairhien of SF commercial hegemony, and is building Andor as a competitor.

By all evidence, the Shadow has largely ignored the SF. There's no doubt the usual 3-5% of DF among them, ready for sabotage, assassinations and the usual the Chosen use the DF for.

The SF did not matter much, they're natural enemies for the Seanchan, much like the Aiel. If Demandred gets involved with the Sea Folk, it will be at Merrilor, and to offer them a Bargain: Windfinders in case the Seanchan invade Murandy against a very attractive commercial deal of some kind. Murandy controls many "mundane" trade lanes.

Murandy stands between Rand's alliance-to-be and the Seanchan. Previously it stood between the strongest (economically and militarily) nation, ally of the WT, and the Seanchan. It holds the key to the "proxy war". Demandred has vast armies of Shadowspawn, Murandy he's secured to one way or another to force the Seanchan and part of Rand's half to fight one another.

Demandred's reasoning is the following: it's no secret Rand wants to unite the Light as one force in one place. That's the strategy he's been aiming for for a long time now. The Shadowspawn have targeted Rand's two largest allies: Bordermen and Andor. Until recently, Demandred could hope the core of the Bordermen armies were caught in Far Madding - don't you think he had massive Shadowspawn armies moving to strike at them there before Rand came to snatch them away? Striking at the heart of Andor, he forces Elayne to choose between remaining in Rand's alliance or returning to Andor. She's really short of allies right now. The Aiel won't come, Rand won't have the Asha'man go except to deal with the WG and evacuation. Egwene has mobilized the WT armies, but she's made a political mistake: in TOM she had handled full control over military decisions to the Hall, and she'll soon be reminded of that. Roedran has already made a clever move to demonstrate he trusts Elayne of Andor but not the White Tower... Roedran is about to offer a defensive pact/alliance to Elayne: his armies come help her free Andor of Shadowspawn, she promises Andor's might, cannons, the Travekkers etc. will stand at Murandy's side if the Seanchan try to invade Murandy/Andor (both have a common border with Altara). He might try to bargain Zaida into it (and if there are high ranking DF near her, or she's one, he might be able to secure part of the Windfinders).

Rand won't get the rulers and their armies to stay united until he strikes unless he has a plan to avoid another Caemlyn. He had foreseen such an attack, but expected it to occur in the South instead. He must have a plan to counter what he had foreseen: Demandred seeking to scatter his forces to be able to take each out in turn. It sounds like Rand's plan is "strike immediately at SG to stop that strategy of the Shadow, evacuate to Merrilor the people who get striked at in the meantime, and don't worry for the cities, they're just stones". He's probably gonna have to accept his "ideal scenario" of striking immediately after Merrilor is not acceptable to the rulers and Egwene, the WO etc. They'll force him to delay to evacuate their cities, send country folk on their way to stedding etc. The best Rand might hope from Egwene and the break is that they accept to commit all the armies and channellers to his Strike whenever he says he's ready with his plan. That's the flaw in Rand's plan: he seems to believe the Pattern will provide him the answer soon. He's wrong, he believes with Merrilor he finally has gatherd the north-south-east-west together "as one". He has not. The answer will prove elusive until he brings the Seanchan together with the other half "as one" - the Pattern won't let him strike until the full conditions for victory are met. In between Merrilor and the Seanchan joining the Light will be the "New War of Shadow" phase of the LB. The alliance with the Seanchan won't happen early in the book... by chapter 11 Mat just arrived in Ebou Dar and hasn't even met Fortuona. And he's not going to sway her with any "honey, we go north". At the moment the only believable scenario to sway Fortuona is sheer despair and facing annihilation from the Shadow. Even "the Shadow has launched the LB and has already razed Andor's capital" won't sway her. Demandred nearly defeating her forces will. And one way or another we have to account for the plan Egeanin and Egwene are about to hatch, and it seems obvious it would involve spreading among Seanchan the information all Seanchan power rests on a sham, that all sul'dam are damane, all the way up to the Empress herself... It sounds to me Rand will get out of Merrilor a "forget the Seanchan" deal - they were stirred by the Shadow once and I've dealt with that. Mat might bring them to us, or else they'll be irrelevant. Leave them alone unless they attack. But Elayne and Roedran will make a defensive pact, and Egwene's will send agents to undermine the whole system. This could mean the Seanchan will not only be drawn in a war vs. Murandy/Andor, they will during it start to see Fortuona's rule and the damane system begin to crack... That could be how they find themselves unable to continue the war against the Shadow and Mat convinces Fortuona her only remaining salvation is to ally what's left of her forces loyal to her to Rand's in the north. Tuon will leave south the faction of High Blood that means to topple her and slaughter all sul'dam (Demandred's forces will wipe them out) and bring the rest to an extremely uneasy alliance with Rand.

That may be why the Seanchan leave the Westlands 5 to 10 years after the LB to reconquer their continent: the Shadow will have razed their fledging Westlands Empire.. Ebou Dar, Amador, Tanchico: gone.