lol you better get real comfortable with ki pulsing (R1). It's the heartbeat of the game. And yes, Ki = Stamina. Ki pulsing allows you to replenish some of the ki you just used attacking. It also allows you to purify yokai realms (dark clouds/puddles on the ground). You want to clear these puddles out as often and quickly as possible. You standing in them will make your ki replenish much slower than usual, and enemies standing in them makes them even harder to kill. Also, there is a skill that allows you to ki pulse while dodging. Depending on how you play, this is a very useful skill.
And the different stances is what allows this game to really open up. Once you start unlocking skills and figure out how to effectively switch stances, the combat really begins to stand out. This is not Dark Souls, nor is it Bloodborne. I think where alot of the hate/criticism of this game comes from is ppl that try to play it like those game: staying in one stance and pushing square or triangle the whole game. lol that is not Nioh, and you're barely scratching the surface of the game if that's how you approach it.
I also wholeheartedly disagree with you saying the controls are clunky. There's a lot going on for sure, but they're very intuitive IMO, and eventually become second nature. The problem is you gotta put in time and be willing to learn a bit, which most ppl don't really wanna do with video games. And that's fine and completely understandable. But at the same time, there are ppl that take that approach, then turn around and paint the game in a negative light. Nah, that's not gonna fly.