Actually, if you took all the flashy combos out of Nioh, you'd still have a more interesting stagger mechanic with permanent ki damage on demons and the corrupted ground, more interesting status effects and buffs that do things besides 15% more damage, a much, much wider variety of basic weapon attacks, more meaningful equipment, the living weapon transformation and it's effects, locational damage on enemies and bosses, and a better NG+ system.
None of that means a whole much for me because we are talking about quanity vs quality.
I happen to think that the basics of FromSoft games are qualitatively superior. This is why i brought up music as an analogy, because you can compare the number of notes and chords all you want, but that tells you nothing about the actual quality of the melodies and harmony of the songs. Making comparisons between what's on paper tells you nothing about all the "invisible" intricacies that exist once you look at the actual reality (it's a bit like claiming Deus Ex is infinitely superior to Doom on every level while ignoring the gunplay in the latter is actually vastly better designed).
The attack patterns and movements of enemies in Nioh was fairly "middle ground" compared to anything in Dark Souls. I wouldn't use a word like "mediocre" because unlike some people here i don't have an axe to grind one way or another, but it's still a fact that if you play the game as if it was Souls it's not even remotely as good. The design of the attacks in FromSoft games are in the main more clever, more unique and look better visually.
Nioh just felt fairly middle of the road in terms of what it does that is similar to Souls. Was better than Dark Souls 2 but in a way it reminded me of the latter, just not as janky.
Now, would the addition of all those other intricacies like combos etc tip the scale, putting the game above FromSoft combat? Maybe. I wish i had seen it but like i said this idea you have to wait until NG++ or whatever in order to get to that part is to the detriment to the game. But from a visual point of view alone, i'm not really keen to what i'm seeing. That guy doing all those spazzy combos in that video i just posted. Might be impressive in terms of gameplay design, is still not particularly appealing to me as a matter of preference. I don't want to spazz around doing animu combos with magic shit shooting out everywhere.
One of my favored fights in Sekiro was this dude:
It's not even a major boss, just a minor mini-boss. But it's the whole visceral feeling i had during this fight. The second he hits me i got so mad (doing a no-hit video on this one was obnoxious because of his buddies at the start) that i just pushed him into the corner and basically pulled some next level (for me anyway) deflect-fu just out of sheer rage.
I never felt this level of intensity when fighting anything in Nioh. Even when i kept the fights simple, the combat didn't feel to have as much "weight" to it, felt more arcadish and less grounded.
Would i feel something similar if i was doing all the DMC style crap that guy is doing in that video? Maybe, maybe not, but just aesthetically i can tell you that kind of thing alienated me a bit. I could still probably enjoy the game by simply accepting it for what it is, but if Nioh 3 and Sekiro 2 were to be announced toghether, my money would go to the latter first, purely out of personal preference.