I keep seeing statements about THAC0 being/not being hard, or taking/not taking more time...I can't remember any person, in my whole dnd playing life, criticising THAC0 on the basis that it is hard to do/use, or that it takes longer.
The criticism is that it is a silly system, that some people find counter intuitive to remember, and others just find annoying on the basis that there is no reason for it to work the way it does, and nearly any other system would be strictly better.
And it's not just young people today, or people who are used to other systems. These criticisms were common, IME, when 2e was still the current edition. The group I started in used THAC0, but then the group I played with right after them used the same system as Alternity.
And rolling under made sense to me, and the other, slightly newer player. I was like, ok negative bonuses is still just...weird, if nothing else, but fine, at least when I get better at something the number increases.
Then, when we finally gave that up and switched to 3.5 (skipping 3.0) it was like Christmas. Finally, the system wasn't designed like it was trying to keep out the dirty casuals, or by a guy who was too much in the weeds to really take stock of the system's idiosyncrasies and see if they were actually worth keeping or not. I was never convinced it wasn't both.