I don't have fond memories of THAC0 but I'm not sure it constitutes illogical or poor design. Good design should teach you about the game and the mechanics behind it. Learning that everybody is working from a base AC of 10, teaches you that the system is designed around a d20, which then lets you know that range by which every action is working and modified.
The way 5e does it is certainly more 'playable', but so much of the intent behind the rules and their design relies on people knowing what came before at this point that I don't know if it does a good job of teaching people why they're designed the way they are. I guess this is a about THAC0 against 'bounded accuracy' neither of which I would choose over 3e. I'm pretty biased towards 3e, I liked how everything was accounted for in it. Then again, every way of doing it leaves me dissatisfied in one way or another.
