I really hate this argument. You can play an all-halfling (or whatever) game just fine with fixed ability modifiers. Not every pc needs a maximized prime ability score for their class; they never have, but especially in 5e, where the math is bounded, you really can do just fine without an 18.
"I want to be able to min-max my stats" is, to me, not a good argument for detracting from the meaningfulness of what is supposed to be one of the main building blocks of your character.
I'll tell you a story from my own experience:
We did a little one-shot adventure to fill in the backstory of a character. Everyone rolled up Goliaths to represent members of a Goliath hunting party. Another guy in our group really wanted to be a Goliath monk, fitting into the idea of the Big, Strong Brawler.
He felt incredibly ineffective.
In a later side adventure he rolled up a Halfling Monk. He said he felt so much more effective as a Halfling Monk, due to the Ability Score Improvements, than the Goliath Monk.
The Ability Score Improvements got in the way of his character concept.
Now I've been playing a Dwarf Wizard in the same campaign. I created this character a while back, so I accepted the fact that I would start with a 15 Intelligence. I specifically chose spells that didn't require Saving Throws or Spell Attacks (like Illusion spells), and chose to be a Divination Wizard so I could save those Portents for when I really needed to hit. Until 4th Level, my Constitution was higher than my Intelligence.
I've had a lot of fun playing this character! It's the very definition of playing "against type."
However, let's say someone else wanted to play a Dwarf Wizard. If they went through all the same hoops I did, they would just have... the same Dwarf Wizard, playing against type. On the other hand, they could use the Tasha's rule to just have a high Intelligence, and be an effective Evoker or Abjurer or whatever.
I don't really see a big deal in that.