Exactly how hard is heihachi?

I'm planning to spend some time learning heihachi and I was looking at some old guides and preety much everyone agrees he is extremely hard. But realistically how hard is he?

I have a couple of high rank characters so learning anyone with the prowess system is always a pain but I'm trying to prepare myself for how much work you need for heihachi in 8.

I never played him in 7 and I know he is very different this time around. However I do main kazuya so the generic electrics and wavedashing work is done and I know heihachi does not have Kazuya's simple 50/50 gameplan. But still I'd like to ask how hard is heihachi and what is his gameplan?