I'm of the opinion that the only reason why ASI/Feats were tied to class levels in the class table, was to make everything less confusing and less having to look up 2 tables like you did back in 3e.
There's also the fact that classes are still front-loaded, even with the new rules. Taking 2 levels of Rogue gets you a HECK of a lot of value that auto-scales over time (i.e. Expertise), so with math being so flat, it becomes sub-optimal not to multi-class for many builds.
It's become increasingly clear to me that the biggest problem this edition tried to tackle was how to go back to a 'class-based' game, with all of it's flaws (Hi, Tony!), and flatten the power curve enough so it became 'linear' and they didn't create accidental 'square' or 'cube' progressions that plagued 3E.
Intending that every single part of the system is on a smooth power slope is part of it. So, the ones that scale with character level and class level are carefully placed.
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- 3E spellcasting MC sucked because of being capped to low level spells? Make those scale with character. Oh, now they don't have spells that they can cast with those slots? Create rules for up-casting within each spell, balanced for the fact that MC casters will have a lot more spells known.
- Cantrips lose value almost immediately for characters without multi-attack? Make those scale with character. Oh, Shillelagh can be taken by a martial with a single feat, and become monstrous? Nerf!
- Single-dipping a class is too powerful? Reduce what they get when they take the second class.
- Feats can be combined with class abilities to create monstrous combinations? Make those tied to class level and always come out in predictable times so their value.
I could go on.
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IMO I agree with the reason this thread is here - the game *does* feel a bit feat-starved, and the one at 16th level feels like too little too late.
So instead of tying feats by character level, I'd just give everyone a free Feat at 1st level. (At my table, I'd encourage UA Racial or Skill feats, and Variant Human feat choices would be with DM approval.)