This is what I don't understand. You are saying that a 5% difference is enough to alter the game, force the hand of many people to change the conception of their character (one they might play for years), and change the long standing rules of the game.
5%?! One magic item - boom, that 5% difference is gone. Multi attack, boom the difference is gone. Any hosts of feats, boom the difference is gone. Oh man, the cleric gave the other party members a bless spell, now my 5% is really really gone! Sneak attack, now my damage is not 5% better than the rogues, dang it, my 5% is gone.
That is why I do not understand your side of the argument. I understand if someone wants to get rid of ASI's because they feel it reflects real world problems. I understand and sympathize with that. But to say rework the entire system for 5% because the min/maxers want things balanced in a game that is already unbalanced - I cannot understand that. Especially knowing how intelligent everyone on these boards happen to be.
So you will have to forgive me. I do not understand.
PS - I do understand that it is not exactly 5%. I am using that as a standard basis for a +1 modifier.
This seems to be because your thinking on this is incredibly narrow.
A +1 magic item? Unless you are a warlock, there are no +1 magic items that give an increase to your spell DC. There are no magic items that let you prepare +1 spells. Additionally, you are assuming the weaker player gets a magic item, and the stronger one doesn't. If it is the reverse, then the difference rises. If they both get a magic item, then the difference stays static. Finally, the game does not assume magic items, and neither do a lot of players. I very often do not give out items with bonuses, instead giving out items with abilities. So the 5% stays.
Multi-Attack? I assume you mean extra attack. So, if we are again talking about two people with the same build, then they both got Extra attack, so I have no idea why you think that removes the difference. Also, casters don't get extra attack as a general rule, so the wizard or cleric does not benefit from this at all.
any host of feats? You mean you took a feat or an ASI? Great, that means the other person did too. So, unless they chose a feat that does not give any bump, and you chose a half-feat (of which there is at least one of each score if you don't mind bending your concept a little) then you are behind. And, like I showed. If both of you increase your score? You are behind. If they pick a feat and you just increase your score, you are behind. The best scenario is them taking a feat that does not benefit the build (giving them versatility) and you have a perfect half-feat to increase your score and get a useful ability. But, feats are so variable it is hard to measure the exact impact.
If the cleric blessed you, then they are buffing you, and that buff would be more powerful if you had better scores... I don't even... ah wait. The rogue gets sneak attack and now your damage isn't better? I see what happened here.
I'm not comparing the Fighter to the Rogue. Or the Wizard to the Bard. I'm comparing them to themselves. I'm comparing a Rogue with 14 Dex to a Rogue with 16 Dex. So, that sneak attack, both builds got it, in the exact same amount, at the exact same time. 14 Dex rogue is still behind 16 Dex rogue. Now sure, maybe it is less obvious if there aren't two rogues at the table, but everyone can do this basic math, and in my expeirence, players with 14's in their main stat are noticeably less effective. I've run a few different character's (player and DM) where this occurred and it was always noticeable.
Then just don't allow goliaths at all. Either do it properly or not at all. In theory an unusually small and sickly dragon could be balanced but those are not allowed either as it would be both unsatisfactory to the players and paint a strange and misleading picture of the dragons.
Then you have to drop everything. Because Variant Humans can be as (Strong/Graceful/Charismatic/Intelligent/Wise/Perceptive/Tough) as any +2 race.
Dwarves are exceptionally tough... as long as you don't count tough humans
Elves are exceptionally graceful... as long as you don't count graceful humans
Gnomes are exceptionally smart.... as long as you don't count smart humans.
So, if that is an issue for you, then you have to drop every single race right now, because that is the current state of the game.