Li Shenron
Legend
I wouldn't overdo this. AD&D2 in particular had a bunch of levels in the middle where it took ages to level up, so much that player characters ended up feeling more or less static. I would not mind this in any other RPG, but D&D comes with the expectation that characters level up every so often.
If it worked differently in AD&D then maybe the expectation is rather on current RPG editions than the whole history of D&D?
Anyway, I have very little experience of AD&D, but at least I know that in older editions there were also many "empty levels" in classes, where the character would advance only with more HP and perhaps better attacks, but no new tactical abilities. The new default in 5e is to always grant something new at level up (although sometimes the 'new' ability granted is still only a numerical increase somewhere).
Unfortunately, I haven't had the chance yet to play 5e until high levels... I have the feeling that the situation is now much better compared to 3e, mostly because the number of spells known by a character is much smaller. But I can say that in 3e the standard XP advancement was definitely a problem in my groups, as we always ended up not even having time to try out the new abilities, and already getting more on top of them.