Oh, I do agree that Piotr's initial appearance in Excalibur was... well, I'm not sure about out of character, so much as jarring. He was clearly a guy suffering from severe psychological problems and anger management issues, but that had been true from before Illyana's death (when she died the one memory I have is him raging at the other X-men for leaving her side before he realizes she's died) and his joining the Acolytes. The way I viewed it was that Piotr had been building and building to that breaking point and it finally came at that moment - emotion, lack of sleep, all these things contributing to his final breakdown which came in the form of anger, not untrue to form (this is the guy who jerked Kitty around and then got into an angry fight with Juggernaut because Kurt and Logan called him on it, remember).
In a way I almost think he needed that violent snap to bring him to his senses and from then on, as you say, he started to return to his former self. But it wasn't just Wisdom keeping Piotr and Kitty apart - it was that they'd grown apart many years before. They were close as friends, but the snapping moment showed the worse of what they could be like as a couple. That's why this return to a Piotr and Kitty romantic relationship seemed forced and unnatural to me.
It's a shame that Fraction seems to have taken Piotr back to a similar mindset he had when he broke down before, his obsession with Kitty isn't so much touching as creepy in his run, in my opinion.