Compare a 5e class to it's AD&D counterpart and you'll see the AD&D class can go multiple levels in a row without gaining anything but HP and attacks/saves improvement.
So what? Gaining HP and attack and/or save improvements are pretty important. That certainly doesn't make a level "dead".
Man, I don't know what AD&D you played, but...
A fighter gains nothing but stat improvement to name level (and an extra attack at higher level).
Wrong. They gain weapon (including specialization) and non-weapon proficiencies as well. Fighters (depending on edition and how you do it) improve attacking every level, which for a fighter is sort of an important deal, right?
Thieves only increase their skill % (and in AD&D, backstab multiplier).
Again wrong. They also get weapon/NW proficiencies, along with reading languages (some do consider tihs along with the other thieving skills) and the ability to cast spells from scrolls. Of course that "only increasing" thief skill stuff couldn't be important to a thief, now could it?
Clerics and magic users get new spell slots, but no other abilities.
Well, proficiencies not withstanding...
And yet their turning undead improves, and frankly magic-users getting spells is kind of their thing, but they can also make potions and scrolls, and eventually (along with clerics and druids) other magical items.
Rangers, paladins, bards and druids all gain few abilities along the way, but nothing like they gained later.
Most of the ranger and paladin (and barbarian, cavalier, etc.) features are insanely front-loaded. Bards get stuff all the time, as do druids at many levels (especially if you go past 15th).
There is no bard songs, no rage, no paladin smites, and wild shape is a 7th level noncombat ability.
THANK GOD!
But 3e proved if you have a dead level, people will multiclass to something that gives treats, so classes all now 20 levels of treats.
Which overloads many players with more stuff than they can remember, if they remember stuff correctly, or let alone use often.
While I can appecaite a "bit more" than perhaps everything AD&D offered, 5E is overkill already and 2024 just makes it worse IMO.