I feel like what Kazuya lacks in pokes he more than makes up with crazy hard punishes and a really good wave dash. The need to practise wave dash, electric and kbd will always be there for any Mishima. Heihachi is easily the simplest Michima to get into, discounting Jin because you could play him completely without any Mishima stuff.
Many punishes work just as well with a normal wgf with most of the difference being between "you fucked up" and "damn, you REALLY fucked up now" regarding the outcome. Not that I'm good enough for either.

Majin seems to be working on his bad matchups. I do think that it helps that he plays King because he goes for many unorthodox plays so if you're mostly used to play against coockie cutter Kings he can surprise you.
I think I need to go and practise a bit with Geese. It's been way too long since I've Raising Strom'd a faggot and he seems to be pretty good.