You literally just used the
Appeal to Tradition fallacy to try and justify a part of D&D.
No, I didn't. I declared that elements of D&D do not need to be justified by verbal explanation for the correct choice to be retention. That the burden of proof for reform has to be not "This part serves no explained purpose", but rather "This part hurts D&D [with actual evidence of harm]".
If you are inventing something
new, "Can I explain what purpose this part serves?" is a perfectly useful design heuristic. But if you are curating something that is already successful, in a universe where most new things fail, it is a very good way to accidentally destroy that success.
Elements of something that is successful are justified by the simple fact of the success of the whole, whether or not anyone has a good verbal explanation for them or how they contribute to the success. This is because people are not omniscient, so an inability to explain an element's contribution does not mean it does not contribute. The argument for
change accordingly needs to be
actively justified.
Changing THAC0 easily overcomes this simple placement of the burden of proof; it demonstrably didn't work well. While mathematically clever, it's easy to demonstrate that real people, en masse find subtraction harder than addition and addition harder than counting, and that people regularly flubbed the calculation in play.
If you've got an argument that halflings are actually confusing to players, or cause problems at the table, like THAC0 did, then you've got a case against halflings. "I don't know of a justification for including them" is not one.
And even then, actually, your argument isn't that you don't see any justification for including them. You simply don't see the justification (supporting people who want to play hobbits from Tolkien) as personally compelling. That's an even weaker argument for excision, given Tolkien's works are popular enough they're not just still in print (in multiple editions), but actively producing spinoff media (a TV series) to boot.
Ah, no. That's what happens when you try to make D&D a video game.
That's a theory as to what exactly went wrong with that implementation, sure.
However, in any case you're applying to halflings the exact same logic that drove 4e design, as you would see if you read the books
Wizards Presents: Races and Classes (December 2007) and
Wizards Presents: Worlds and Monsters (January 2008). I accordingly expect applying very similar logic to the same task (revising D&D) would produce similar results (commercial failure).