I preface my remarks with this: I have to concede that real world evolutionary biology simply does not work within the construct of the D&D stat generation.
Now, that being said:
I hate Tasha's for a number of reasons (not power creep, but power leap, in many classes and subclasses), but fundamentally, the floating ASI is totally ridiculous. It has long been established what power-gamers can do with it. I am coaching a new DM, and because stuff like it was allowed, he is now struggling to match combat encounters to the actual strength of the players (level 3).
But what burns me more is the silly notion that certain species can't have certain starting abilities that are higher than starting abilities of other species. To suggest that the weakest Polar Bear that survives into adulthood can be weaker than a chipmunk, or a human, is completely ludicrous. That is simply not how evolution works.
So to suggest that the strongest Gnome can have a higher strength than the weakest Goliath that survived into adulthood....well, equally ludicrous. But, as I prefaced though, evolution does not translate well into D&D. But under no circumstances does a Halfling start with an 18 in Str while a Goliath is 8.
I would suggest that the floating ASI can be allowed, but ONLY if every species has a unique base level of stats.
The only way floating ASI's can be applied is if two conditions are applied:
1. Each species must have a minimum level of starting stats, be it via the Std Array, 27 point buy points being applied, or even rolling stats (once again, a favourite tool of powergamers). A Goliath has to manipulate their stats so their Str and Con are a minimum of 10 at level 1.
2. No char, under any circumstances, can start at level 1 with a stat higher than 17, after all points, feats (I would completely ditch the Human Variant), and ASI's are applied.
Now, point #2 is easily applied, but point #1 raises the hackles of so many...too bad. It means that for the Heinz 57 species (sorry, think there actually 56), minimum species specific levels have to be established in 2 stats. Example: A Gnome must have Dex of 10 and a Int of 10. A Halfling must be Dex =10, Cha = 10. A Goliath, Half-Orc, and Dwarf must be Str =10, Con =10. Humans are a special case already, with a minimum of 9 in each stat. Which is very very close to fixed ASI's. I am sure there can be all kinds of debate about what stats must have minimum levels for each species, and this also messes with sub-species' stat bonuses.
So someone wants a Half-Orc with a High Int, or a Halfling with a high Str? No problem.
All creatures in the game start with 8 points, right across the board. Using the 27 Point Buy system, each creatures burn 4 points to get their two Species specific stats to 10, then they can burn the rest of the points as they like.
So smart Half-Orc applies 4 points from the 27 point buy to Str and Con, pushing those to 10 each. 23 points are left. 9 are applied to Int, pushing that to a 15. That leaves 14 points to be applied as the player likes. And THEN a floating ASI can be applied of a +2 to one stat, and a +1 to another stat, player's choice. So Half-Orc with a 17 Int and a Halfling with 17 Str can be created at level 1, but said Half-Orc is not going to start with an 8 Con or 8 Str, and there are no 8 CHA Halflings.