Heihachi' lvl1 isn't good to just throw out like say kratos lvl 1. You have to combo into it.
After his foward + square or his cirlce counter you can go right into lvl 1
I've got like 10 kills in one game by just building to lvl 1, blocking peoples square chains they like to spam,
punihsing with foward + square and then going into lvl 1.
Also the counter is really useful for situation where everyone is grouped together and spamming attacks since it hits
aoe around heihachi. Just mash counter and then go into super after it activates.
And his lvl 2 is probably the best super in the game. I almost always get atleast 3 kills with it but often i'll get 5 to 6 kills with it.
His wavedash is great for getting in on longer ranged opponents like kratos and radec and EWGF will beat a lot of other characters attacks. You can kind of just spam it.
The main combo you can go into after his foward + square or counter is...wave dash + triangle(three times) then foward + triangle(for the two hitting kick) then let them fall a little and do down + triangle. This combo builds like 1 meter by it self.
IMO heihachi's pretty good in this game. Not the best but good.