What do you mean his super is hard to get out on reaction? It's the same command as the majority of supers in the game,

,

+

It's not different at all in execution, I've never had problems with it.
You can't really "counter" his 360 because to begin with there is no throw whiff-animation. If the screen flashes Potential Power, you're caught. All your opponent can do is try to find ways to prevent you from doing it, but Yamazaki has his fairshare of ways to set it up. All Yamazaki needs is a knockdown to keep you guessing.
Then, I gotta disagree when you say his combo's are limited. Yamazaki has alot of combo options, especially dizzy combo's and 100% combo's, some of the nastiest (and hardest to do) in the game.
http://www.youtube.com/watch?v=DiKfzAnK0Tghttp://www.youtube.com/watch?v=_Muvs9ByGhIFinally, check out this match, this Yamazaki does alot of great stuff -
http://www.youtube.com/watch?v=-7x1lQWPJ50One of Yamazaki's high level techniques is using his Snake Arm and canceling it (Tap

after you do Snake Arm), and this gives him an instant recovery, far faster than your average feint cancel. You can do crazy stuff like if your opponent is attacking you and your blocking, do a Snake Arm Breakshot, cancel it, and then P-Power them.
And it also allows Yamazaki to do a sort of "loop" -
http://www.youtube.com/watch?v=ePR6px6Kyh8Yamazaki is powerful, but he really needs high level execution to take advantage of his greatest techniques. I've seen alot of crazy Yamazaki players on Supercade years ago, very scary shit... one of my pals Caddie dabbled with Yamazaki, he was very consistent with finding ways of landing his P-Power (He typically mains Duck King/Geese/Krauser, all have 360 grabs, so Yamazaki fits into the puzzle quite well).