You give them too much credit for this aspect in particular. They didn't have the book to reflect in depth on that at the time.

It's no mystery why they split the books as they did, as they explained it all. Brandon wrote Egwene's and Rand's storylines first and was well into that when it became obvious there was no way he could finish the full book in time for the date Harriet had announced, and Harriet and Tor were ready to give up on that when Brandon came up with a last minute solution to resuffle the chronology of events planned by Jordan and focus a first volume on the two storylines he had written, gambling on the fact the rest he had not written then would work as a second book. It worked rather well for the first two storylines admittedly, no surprise there as Jordan had planned for the storylines to run in parralel (!) but it ruined many aspects of the rest.

That was a very high risk gamble to take at that point. It wasn't his material that he would have known more intimately, and he couldn't really see all the subtleties of the dramatic progression and structure before he had completed the whole story and could take a look back at the whole thing (I'm 100% certain Brandon wouldn't have split the book as he did if he had written the whole thing first). He just couldn't see either what he might be missing in terms of story subtleties, or small appearances by secondary characters to bring final resolution and so on. A lot of that is added once the complete first draft is all done. He evacuated most of those players from TGS, and it was too late for that when it came to TOM, with the result a great deal of Jordan's side elements turned out very disappointing - like the finer elements of Tower politics for example. Alviarin is also one of those whose build up over several books got totally ruined by Brandon, same for the BA hunters. Alviarin playing no role at all between the end of KOD and Egwene's victory over Elaida and over the BA, that would have been called an idiotic theory if someone had proposed that before RJ died. But it's exactly what Brandon did.

And the results of the book split is what we got, a more than decent TGS and a really bad TOM (individual episodes in it are good, it's as a book it really sucks) We can see how Jordan built his finale so all storylines progressed in parallel until Rand's epiphany and the various other climaxes came together, and joined afterward. Before the epiphany, it looked as if everything what spiraling toward doom. If you tell some of these episodes after the reader knows it will all get solved because of the epiphany, it totally changes the interest and perception of these events. Brandon has done a lot of good things with the books, but the structure of the story, and the dramatic impact of a very dark beginning followed by a series of climaxes before the epic "real" finale began, he totally ruined.

Jordan didn't work like that, writing by storylines and all. He didn't split or regroup the scenes into chapters either before it was all finished, and it's only then he worked with Harriet to establish in which order the chapters would go, like assembling a puzzle. You can't do that job well without having the global picture in front of you and actually be able to read to see how it all fits and flows, if some scenes aren't missing, or if some scenes are redundant...

That was a really bad move to start publishing bits and pieces of a story meant to form one book when it's only 30% written. Jordan would have known why he had Perrin or Mat do this or that at what time and why, and how it connected thematically with what happens to Egwene or Rand and so on. If it were his book, Brandon would know that too, and would have known splitting it as he did came with a heavy price for the rest of the story to tell.

His next big mistake was to realize (too late), he couldn't well just abandon Rand and Egwene after the big events of TGS, so he had to reintroduce them early in TOM, out of synch with the rest of the players as they were several weeks ahead, which was ok dramatically speaking (forming bookends, so to speak) but ended up creating complete abherations in the various timelines, like having characters like Elayne show up in various scenes totally out of chronological order (that's OK for flashbacks or forward, or to create stylistic effects with time, but in traditional storytelling, it's considered terrible writing to do anything like this, a first novel kind of mistakes, unforgivable for people of Brandon's and Harriet's experience and if they cared to be honest, they'd probably admit it's like that because they had painted themselves into a corner the way they split the book).

There's no way to know if Jordan would have grouped the chapters more and how he would have paced it all (probably more grouped, but as the pace of events was accelerating, probably not quite as much as in the last 2-3 books, more like the mid-series) but Jordan would also have written significantly less chapters and scenes too - he did much more in a single scene than Brandon did, different styles of storytelling there. Instead of several Aviendha POV in TGS for e.g. (where she ends up thinking the same things using different words, really), she would have had one, her little problems with the WO being seen in the background by Rand or Min during other scenes instead. Jordan disgressed briefly a lot in nearly every scene, but often these disgressions to notice things in the background (or report rumors and news) saved him many on-screen full length scenes later).

It's very clear he would have followed the chronology of events far more than Brandon did (as he almost always did, and did systematically when it had dramatic importance to do so. His only big mistake was showing the Cleansing too soon to have a climax in WH, and we all know the price he had to pay for that with COT) and avoid "spoiling" the dramatic impact by going too far in one storyline (Rand's) and letting all the others too much behind. It's no doubt in part why he was so adamant that this story was really conceived to happen over the course of a single book to be great, that he saw to way to divide it in more than one book and keep it as good. It's this Brandon and co. overlooked, that the story was developped and planned by Jordan to be told chronologically even if it had to be split in volumes afterward for publishing if necessary.

Jordan's chronology was to have the Seanchan attack followed by Rand's epiphany, It's pretty obvious (I think) that Mesaana was to strike right away after Egwene won the Tower (this was delay only to get Egwene scenes in TOM and synch her up for her encounter of Perrin)- not weeks later, with Perrin coming with Slayer during this confrontation, and witnessing Rand's epiphany in the aftermath, to return to his camp and forge his hammer. Then came Mat's rescue of Moiraine, and Elayne taking the Sun Trhone. Pretty much all one after the other, or cutting from one to the other in parralel (Aviendha's trial in Rhuidean fit in there too, pre epiphany by the timeline). The effect Jordan was aiming for his obvious: Rand's epiphany suddenly unlocked the Pattern and all was happening at once. Then bang, the Shadow striked back and the LB began as Rand and Egwene were still arguing about the seals.

We know Perrin's storyline began in the original prologue (it had four scenes written by Jordan himself in there, one of Perrin, one of Faile, one of Masema and one of Galad) The material written for Mat and Perrin in TGS was largely invented by Brandon (and just slowed things down for the sake of showing them at all in the book). This right there made Perrin jump ahead two-three weeks in the timeline over the course of those scenes, and economically synchronized him with Semirhage's capture, the scene with Rand Jordan revisited in the prologue (then Rand jumps ahead a few weeks). Very likely, Jordan meant to start with Perrin and Egwene - the most behind - to pick up with Rand in AD a bit after, and introduce Mat, who was ahead of the others, and Elayne who was roughly on the same timeline as Mat, later in the books when Egwene, Rand and Perrin had caught up. It's also fairly obvious reading TOM that Jordan meant Perrin's storyline before the reunion advance faster. Brandon stretched it out with redundant scenes (less so for Mat) because he needed to make one book out of what was left. The bottomline: pre-TG AMOL was to have a great deal of Rand and Egwene, not nearly as much Mat and Perrin whose last story was much simpler, and almost no Elayne.

We will likely never know if Mat was to meet Verin on screen. I doubt it personally. That scene worked as a teaser/stopping point, but didn't serve a purpose if Mat's storyline was told continuously. I think it's quite possible, even likely, Jordan meant to surprise us by picking up the Mat storyline with him already encamped outside Caemlyn and we learned Verin helped him get there and how, and left him these mysterious instructions (that's more Jordan's style of storytelling, and actually, it is the first Mat scene for the book he left. All he wrote and sketched for Mat in AMOL began with that, and I get the feeling Jordan meant to start there with him). That scene where we learned Verin met Mat and brought him faster to Caemlyn chronologically happens later in the book (about a third into it, probably), and would have served as the teaser to make us wonder when and where Verin would show up in person, and it would have turned out to be at the Tower in the nick of time.