It certainly isn’t complex, but it is absolutely poorly designed. There is a MUCH cleaner, more intuitive way to go about combat, which is what D&D thankfully evolved to.
My personal opinion is that the current system is not ideal either. The fact that you can continue to increase the factor by which you avoid being hit, to unreasonable levels just sits wrong with me. I don't care how magical your armor is, or how good you are at fighting/dodging, at the end of the day even a zero level scrub should be able to hit you. Now, taking damage? that should be a different story.
A 20 still always hits, regardless of everything else.
But I think if you are at the point in the game where you might have a 20+ AC and you are regularly (or ever) fighting extremely weak enemies, the DM is doing something wrong, because that isn’t fun in any system: 5E or AD&D 2nd Ed. Because of how long combat takes on table top, I always think it’s important that I am not wasting my players time.
If it’s a matter of just hypothetically it should be possible, I don’t think concerns beyond the practical implementations of the rules are valid, but we are both entitled to our opinions.
I’ve also really come around on 5E’s attribute system. I don’t even have my players roll stats stats anymore. Point buy makes for a balanced and engaging experience where players are making interesting choices at character creation and as they develop and level up. And while I don’t mind playing characters with dog shit stats (I just played one recently and it was great), most players don’t want this, so I’m happy to not need to deal with their disappointment.
