I agree something was missing with Aran'gar, but I disagree on what it is.

The foreshadowing was in KOD. Aran'gar meant to use Graendal's networks to get Rand killed and put the blame on her.

That made a short-lived return in TOM, barely touched on (I might eve imagine this!).

The thing is, Brandon had most of Egwene's story mapped out for him by RJ. We got pretty much everything, it's only Alviarin,s storyline that was obviously missing, with a remnant in one scene RJ must have drafted himself. It lead nowhere.

For Rand, Brandon had many more holes, and obviously he filled them as he could. The Graendal/Aran'gar story arc, Brandon just failed to make very good use of. It's conceivable it didn't matter that much to RJ. It's Rand's progression that mattered, his whole storyline was a fall into insanity, then the Epiphany. I could well imagine RJ left the details of where we'd see interference from Aran'gar, and where we'd see hints of pawns of Graendal for later, when he crafted the details of the storylines, the plot that he would build around the character development. The details didn't matter that much, Graendal would have had a rational plan, Aran'gar would have ruined it and put Rand's life in danger, which put Graendal in dire danger from Moridin. Graendal would have puzzled it out, and it would have played in her final decision to trap Aran'gar in the end.

But RJ needed to get Egwene's timeline set in stone first, as it determined how long Rand spent in AD. Brandon chose not to make much use of Aran'gar/Graendal - perhaps he didn't have much notes on that and didn't think of anything. There was many great things in Rand's storyline, but the lack of depth of the Forsaken plot while he was in AD was certainly pretty disappointing.

For that matter, we see the same thing in Egwene's storyline. The BA plot and Mesaana were the big disappointment, perhaps because RJ would have grafted those details later on, once he had the protagonist character's progression solidly in place. This was left to Brandon, who didn't find uses for these characters.

I very much doubt Brandon changed the fate of two Forsaken and inversed the one who was supposed to die and the one who was supposed to move on. Sanderson never lists Graendal among his favourite, and it seems obvious he's not comfortable writing a depraved character like her, not very good at getting in her mind. I'm pretty sure he would have preferred another character for this if it was left to him, but RJ killed Aran'gar in AD and Graendal just got enslaved, so that's Graendal he used.

As for the male channeling at the battle, I'm sure this was supposed to be a teaser announcing Demandred's arrival in the plot - that the decision he wouldn't reveal his channelers just yet was his decision. Slayer failed, Moridin immediately ordered Demandred to send in the army. But Demandred didn't want to ruin his surprise at the BT, so ordered the channelers to stay out of it.

Brandon changed that so Graendal called the army. He didn't want to get to Demandred before AMOL, except for the epilogue.

For Byar, I agree 100% with you. I'm sure it was a change, and it wasn't a good one. It ruined the character. That he wouldn't accept the decision of the LCC and let his hatred get the better of him and attempt to kill Perrin was foreshadowed since their first meeting or so. Turning that to Compulsion was a bad idea. It's just as if Jordan chose to make Aram a DF, or compelled by a Forsaken. It would have ruined this storyline. Brandon just ruined the repetition of that motif again, with Byar. It's no big deal, just a bit annoying for re reads and such, where Byar's build up through the series will feel really irrelevant (much like Alviarin's build up is now totally ruined by forgetting to use her in TGS...her involvement with Mesaana, her efforts against the BA hunters, how she started to approach Egwene.. it will all feel very "blahh" now.)