Yup.

By KOD, Jordan had brought to Mat a gravitas and a fatalism he never had before and Brandon discarded all that completely. He was no longer a stupid immature teenager, and even Jordan's Mat humor was darker and darker. Sanderson decided to send him back to childhood, and did it in a most unconvincing way. But it was other aspects of his character Mat was to struggle with. He was still keen to avoid work, still hated battles and responsibilities, and his wedding to Tuon now constrained him over some of his favourite activities, like flirting. As for his fears of Rand and being around Rand, this had not changed. It had grown worse and worse through the series (his last scene with Rand, when Rand came to order him to Salidar, was very revealing of Mat's feelings. Mat already was afraid, and convinced Rand was insane.).

What Jordan seemed to work his way to was rather to make Mat break under pressure coming from all sides.

There were a series of things RJ had set up, that Sanderson either didn't use or didn't use as they could have been used. First there were the games of Joline. Sanderson decided they were red herrings, but RJ rather pointed in the direction of Joline making a foolish attempt to steal Mat's medallion and bond him Alanna style. A failed attempt, but one meant to rekindle his feelings about Aes Sedai. Then there was Setalle Mat liked well enough, but who was more and more... motherly. Then there was Verin trying to entangle and manipulate Mat. An then Thom pestering him about Moiraine and Ghenjei. And Moiraine was still her "ah, ta'veren" self.

The more Mat advanced north, the more he found himself entangled in "bloody Aes Sedai business" and string pulling.

In the Ghenjei scenes written by RJ, Mat has already decided, and made sure to tell Moiraine before she got ideas in her head to force him to come north to Rand, that he intended to head south to Tuon, that he had no intention to go to Merrilor. He meant to go back to his camp in Andor, and from there head south (which he did offscreen, he didn't have Pips with him at Ghenjei).

Mat had prepared his final flight... it's most likely why RJ meant him to relinquish the Band of the Red Hand to Elayne, and his responsabilities for Olver to Setalle. He had decided not to open the letter, and all he had left was his bloody promise to Thom he couldn't wriggle out.

The final clinchers were probably the whole shock of what happened to Ghenjei and then probably seeing Caemlyn in flames, reading Verin's letter left open in his tent and learning it's why Verin wanted him so badly to remain there. Joline, the gholam, the Finns, the bloody Trolloc Wars come again.... it piled up, and Mat took what he had left of himself south.

Instead of taking a deep breath and deciding to head to Merrilor, Mat fled to Ebou Dar with mutterings for Moiraine's sake about bringing back the Seanchan and leaving vague instructions to Moiraine to arrange to send him the Horn of Valere. Then in Ebou Dar it would look more and more like a flight, pure and simple. Mat was done with the bloody Aes Sedai and Rand, his place was with his wife, wasn't it? At least Tuon would keep him out of that. Oh, he would have tried to convince Tuon, half-hearted, that they had to go fight the LB, but when she told him of her encounter with Rand, that he was mad and totally insane, Mat's resolve would rapidly have evaporated. But he would have found himself caught in the Seanchan net, pushed to responsibilities and aghast to find out Tuon meant to launch a major and this time final assault on Tar Valon! Too late for him to flee, he was caught again.

Then of course Mat didn't return, and before SG Rand decided he had waited for him to come long enough - that obviously Mat had either failed to convince Tuon or decided not to come, and he went and fetched him.

Brandon turned Mat's flight and apparent "betrayal", his abandon of his duties and friends, into a massive joke. But it was all the more an important foreshadowing that this betrayal had been foreshadowed in TGH during the Portal Stones episodes by which RJ had foreshadowed Rand's confrontation with Shai'tan.

He abandoned the Band, he abandoned Olver, he abandoned Perrin and Rand, Thom.. everyone who was counting on him. But everyone took all that in stride and Brandon told all this on a decidedly odd and annoying lighthearted tone. A big "Mat will be Mat" joke.

RJ rather clearly intended this as a darker version of the pattern by which Mat tries to flee yet the Pattern yanks him back and put him in the middle of the worse of the fight. It's extremely reminiscent of the Battle of Cairhien. Mat collaborated to planning it, but at the first opportunity he tried to take advantage of the chaos of the battle to cowardly flee and abandon his friends unseen. The Pattern didn't let him, placing armies and foes at every turn, until Mat found himself, to survive this, to leading the soldiers that would join him as the Band, and facing Couladin who rather sought Rand.

Brandon turned Mat into a complete imbecile through his POVs and actions, but proceeded to tell us "but he's actually a genius".

Admittedly, Mat is one of RJ's most complex characters, and it would extremely tricky and full of pitfalls to write him as RJ intended yet preserve the readers's sympathy for him by providing enough justifications for Mat's decisions in his POVs. Probably only RJ has the mastery of the character to pull this off fully convincingly, and the balls to do this with Mat. But it's quite manageable, Lucas did the same with Han Solo over and over, and it worked. What made trickier was to do it at the end of the character's arc, which Lucas didn't do. He had Solo do it at the end of ANH, and again planning to in TSEB, but he didn't do it in ROTJ. But RJ would have pulled it off, I'm quite sure. He lead the majority of the fanbase by the nose with Mat. It's baffling how much he got away with, with this character. He made us fall over and over in the POV trap with him. It's only fairly recent I've spotted all the evidence that the famous "holes in Mat's memories" were essentially an invention of Mat, and how RJ pulled it off and left us the clues to puzzle it out (essentially it's to hilariously pair up a mention of the holes by Mat with extremely specific and detailed memories not much later that totally contradict Mat's beliefs. The events he thinks he misses simply never happened. All Mat has no consciousness/memory from is his state while under the power of Shadar Logoth, that and the few times he was so fevered and out of it he wasn't conscious anymore of what was happening - and those times are few and far between... parts of the few last days before Moiraine healed him, and the very last part of the trip back to Tar Valon.). Mat was always thorn between a desire to be special and fearing what being special meant.

A big turn point when Mat invented the biggest holes is after he met the young Tairen Lords and realized how boring and repetitive his Two Rivers life had been. Instead of admitting to himself his life had been milking cows and doing chores, fighting with his sisters, playing pranks and having the occasional fun with his friends, Mat decided "all the good bits" of his life were gone!
Mat not only convinced himself this was real, but he convinced most of the readers it was real.