Okay, so here's the thing. Whether or not THAC0 and descending AC are hard or difficult or even complicated is a matter of personal experience. That's different from an opinion; that these systems may have been simple and easy for Amy but difficult and complex for Beth is, in both cases, completely factual. Does that say more about the players than it does the systems? Maybe, possibly not. I think anyone blaming Beth and telling her to get better, to just figure out, it's not that difficult, would be, very rightfully, accused of gatekeeping at worst, and just kind of being a jerk at best. But it's also true that different people have different natural and practiced skill in quantitative reasoning (and even in very different types of math), and it is certainly true that the more intuitive a mathematical system is, the less the "skill gap", for lack of a better term, gets in the way of actual understanding.
Here's a thing I would like to think most of us would agree with: BAB and ascending AC is a more intuitive set of systems than THAC0 and descending AC, especially given both systems were roll-over, not roll-under. While it's certainly possible to have had a different experience, I would also like to think that we could at least agree that this would be an unusual or at least fairly rare experience. I mean, I certainly have my own personal processes that I'm so used to and more comfortable with regardless of the existence of simpler, more intuitive processes.
I mean, I grew up with THAC0 and descending AC; I figured it out and used it because that's all there was. When I first read 3.0 and saw how they changed it my initial reaction was "Why get of THAC0?" and my immediate follow-up reaction was "wait, no, this actually just makes way more sense". But that's not going to be a universal experience.
