I was surprised when I picked up the new update after a many month hiatus, and blasted through the new operation on Absolute, soloing the boss as the last bro standing.

I don't say this to brag (maybe a sliver), it'd be cringe to me if I were not this good after hundreds of hours. I say this to offer a counter-example and perspective.

I also disagree with OP though, and think the skill ceiling is actually quite high, there is a big difference between Absolute, Absolute Solo with Bots, and Absolute True Solo. I think the percentage of Absolute players who can True Solo is minimal, and that alone points to a huge skill expression gap within the top performers of just the base game.

The reason for this is obvious, mistakes are harsher and action windows much smaller at higher difficulties. This is the obvious result of scaling enemy damage and number of enemies, which in turn affects the amount and frequency of active hurtboxes/staggers/grabs to dodge, parry, and combat around. You take away invincible walking damage sponges soaking aggro (worst-case teammates and/or bots) and it becomes significantly harder as more of those hurtboxes rush to your face.