Here's the problem I feel with any sort of bonus or penalty to ability scores system you have in the game... once characters are created, none of them matter anymore.
The whole point of minimums or maximums or bonuses or penalties is to distinguish how a race on the whole compares to humans. If you take a large swathe of everyday elves... they will more often than not be more dexterous that a similar large swathe of humans because of their bonus. The problem though... is that PCs aren't average. None of these perceptions that elves tend to be more dexterous than humans applies to PCs because once you introduce rolling or point buying ability scores, the bonuses or penalties disappear once the character has been made.
Case in point-- a person makes an Elf Bard and after rolling or point buying their Dexterity score and applying their racial bonus... the PC ends up with a 14 DEX. Okay. Fine. Meanwhile, the player of the Human Rogue rolls or point buys their Dexterity score and ends up with a 16. All right then. But now... what does this mean once the game begins? Will the Elf's Dexterity bonus for being an elf have any impact on the character or the game ever again in the game? Nope. Not a single bit. ALL the players are going to know and notice is that the Human is always more dexterous than the Elf, and that fact is going to be true for the entirety of the campaign. The idea of the "average elf" compared to the "average human" is washed away because the Elf and the Human in the game are not average elves and humans and the only comparison is to each other. A comparison where humans are more dexterous than elves.
So what exactly did the Elf's Dexterity bonus at character creation get them? Pretty much absolutely nothing. At least nothing they couldn't have been gotten by just re-jiggering the points they bought or the rolls they assigned. So at that point, why even bother? The only time you ever really notice a non-human's racial bonus occurs when that player buys the highest score available for the ability they get their +2 in. Because then and only then are they assured of being "better" than their human counterpart there at the table. But ironically even that usually doesn't mean very much (in point buy especially) because the human PC can still usually acquire the exact same ability modifier as their non-human counterpart. The elf might be able to point buy and racially bump to a 17 DEX compared to a human only getting to 16... but seeing as how they are both playing with +3 DEX modifiers, that's all anyone is really going to care about. Applicable numbers-wise... the elf isn't more dexterous than the human... they both are running around with +5s for their attack bonuses, skills, and saving throws when DEX + proficiency is applied.
At the end of the day, it feels like there should be some noticeable difference for non-humans being a bit better or worse than humans in certain abilities... but once you assign or roll random numbers and apply them however you want... those feelings just go away. So its nothing you really should even think about or bother with anymore.
While I understand the jist of your argument, I think you are not looking at it the right way. First, the point is they
do matter at character creation. Regardless of how you generate ability scores, once you have them, the method used and the racial bonuses applied, etc. is done. But those racial modifiers do continue to matter. Without them, your Elf's DEX 14 would only be DEX 12. Likewise, the Human's DEX 16 would be 15 (assuming a point-buy and +1 ASI for race, not a feat).
In comparison, the human with DEX 16 is significantly more dexterous than most humans and many elves (average DEX 12), as where the elf with DEX 14 is a bit more dexterous than other elves and still very much more dexterous than average humans (DEX 10). Both are 4 points higher compared to the other races' averages (DEX 16 vs 12, DEX 14 vs 10).
When doing a PC comparison, you will find the average elf PC will have a better DEX than the average human PC. Why? Because many players will choose an elf when they want a high DEX. A player who decides to play an Elf Bard is already capping their CHA at 15 since elves get no racial bonus to CHA.
And although you are correct that a DEX 16 human and DEX 17 elf both get a +3 mod, the elf can get the +4 more easily (or, at least get the +4 with
some other benefit, e.g. a feat with DEX +1 or DEX +1 and
another ASI +1). As where the human would have to fully devote the ASI +2 to DEX to keep pace with the bonus of the elf, losing other benefits.
What the elf's modifiers got them was a better DEX. It isn't the same if you move them around (at least not with the point-buy). With point-buy, you spent 4 points to get from 8 to 12, and the +2 mod boosted the DEX to 14. Going from 12 to 14 is worth 3 points of point-buy (12-13 is 1, 13-14 is 2 points). So, to buy a DEX 14 would be 7 points instead of 4. If the DEX was lower, than sure it would be a shift-capable change, but it still means you get to spend those points elsewhere.
Finally, your idea that the DEX 16 human will
always be better than the DEX 14 elf is incorrect. Both have the potential to have DEX 20, even if it takes the elf longer to get there. And the lower DEX for the elf means it has higher numbers elsewhere, better than the human's. This elf is likely more charismatic than most half-elves.
So, while PCs are not average, they are going to have their strengths that might not necessarily coincide with racial bonuses. Nothing wrong with that. There is also nothing wrong with the tables that remove racial modifiers completely. I've argued for that myself. You say elves are more dexterous? Then put a good score there, otherwise your character is the exception and has a mediocre DEX.
Anyway, sorry this is a bit here and there, but even after my morning coffee I am not completely awake yet.
