As someone who finished Insane and Dark Mode multiple times in TW2 difficulty in itself is meaningless, it's the satisfaction of combat, the good design of it that makes a game enjoyable not some random dweb one shotting you because the only way to make the game challenging and thus satysfying is nonsensical difficulty modes, not that W3 isn't already guilty of this.
Sorry but where "W3 is already guilty of this"? I didn't see a difficulty in there where enemies one-shot you (in fact all the contrary since you one-shot enemies through and through), neither if taking you out of guard, from behind and higher level than you and/or bosses (sadly, in fact),
While part of what you say can, indeed, be true, challenge IS part of enjoyment on combat mechanics. Without challenge you can even have the most fun and fluid combat mechanics existent but they will feel void nonetheless, just because there's no sense of achievement in what you do. If that was not the case the best combat mechanic would be a very fluid system where you one shot everything, giving you a realistic sense of what it happens in reality, and yet the best games at combat design do TOTALLY the opposite (or they don't go with the realistic, or if they go with there then they tied it with very slow paced and methodical combat).
I still remember when playing Ninja Gaiden or Beast (the old Amiga) in the past where every level was an achievement. Sure, it was really brutal at times (even too much sincerely as past a point it's practically masochism) but when you did beat those levels, boy if you felt great.
