Exactly. And that's definitely part of it. The players also don't want to deal with wading through all that old high Gygaxian either, so just go with whatever the DM says, which, more often than not, was a kitbash of AD&D and B/X anyway. Whereas now, the rules are readable and the players expect them to be followed...but they are still many and complex in places. So AD&D, as actually played, wins.
Needing to know exactly what the books say about a particular edge case is a modern thing. It barely existed back in the day. Yes, we had rules lawyers, but they were nowhere near as ubiquitous as today. And they were mostly concerned with spells. We always did some version of +/-2 through +/-5 for d20 rolls and some version of +/-10 through +/-25 for d100 rolls. Keeps is simple and no rules look ups required.
The difference of course is one's official and one's not. If that matters. And it really, really does for some.
So your argument, and correct me if I'm wrong, is that the rules were so bad nobody tried to use them? That's better somehow? Am I the only one who remembers the various charts of what weapon did what damage against specific armors, or certain weapons did more damage to large creatures or ... well the list goes on.
Just because the rules were such a mess that you couldn't follow them didn't make the game easier to run IMHO. It just meant that you kind of made it up as you went along. We also tended to do more dungeon crawls, the list of classes and races was significantly smaller (all depending on exact edition and options).
If you want to keep things simple, just use the basic rules. No feats, no multiclassing, limit classes. Do dungeon crawls where you run around kicking in doors. At that point you have something similar to older versions of D&D and yes, it's similar difficulty IMHO because if you care enough to actually use the rules they make sense. In my experience, I've encountered fewer rules lawyers in 5E than I did for at least the previous two editions, and probably back to AD&D. If anyone ever questioned anything at the table in 5E the DM just made a decision (which occasionally meant looking up a rule, because that's actually possible in 5E) and we moved on. Lawyers, including rules lawyers, will always be with us.
YMMV of course, but that's kind of been my point. We'd have to find someone that picked up the book at a game store and started playing with minimal guidance like we did back in the day to answer these questions to know. Without that we just don't know. All we do know is that the game sells well and that, like all things, the DMG in particular could be better.