I simply don't agree with "if you feel species X should be better/worse at a thing, just assign the individual character a better/worse number at the thing." Again, splats need to mechanically define things or they have no reason to exist. The game don't just say "Any class can take any spell, if you don't want wizard to be able to cast healing magic, just don't take healing spells for your wizard."
It could be a personal background issue. I started with BX/BECMI where races didn't have stat bonuses or penalties (although they did have speed and polearm issues), and later went to the AD&Ds where halflings pretty much had to find gauntlets of ogre power before they could credibly play fighters. Also had a female gamer that wanted to play a Red Sonja/Wonder Woman type character and ran into the AD&D Str rules and the boys going 'it's just realistic that you can't play a good woman fighter, why don't you play a cleric?' So I'm relatively suspicious of 'it just makes sense' stuff. Regardless, I think that a Strength 20 represents being able to do certain things. If you don't think a halfling should be able to do those things, I think the reasonable solution is to not play a 20 strength halfling, and worldbuilding-wise not have a lot of 20 strength halflings wandering around (but the player who wants to play a 20 strength halfling, and has fullfilled whatever game-price-paid necessary to get it, that's the super-outlier halfling, and I'm not sure they need any special side-penalty for wanting to do so.
As to splats needing to mechanically define things and wizards not casting healing spells, I don't see how they are relevant. Things are allowed to have boundaries. I'm saying I do not see a strength limit (or penalty at character creation) is a boundary that adds to the game. At least not in the new paradigm where most gamers don't want to restrict certain races to certain subsets of playable roles. Class role boundaries are a separate category of boundaries and, for the most part (healing magic in particular seems to be spreading out like spilled oil), is still being considered a primary set of limitations within which an individual character can work (barbarians limited to str-weapons and rogues to dex-ones being good examples).
But I agree that representing these things well is hard, especially if you want to keep all species equally viable for all classes. I feel there is a fundamental design flaw with ability scores and how they're tied to classes. Granted, the strength is least of the issue, as you can actually function well without it, even as a melee combatant, except as a barbarian.
I'm rather vocal about thinking that the game would work better if attributes were mostly separated from primary-class-function and mostly cover things like skills, maybe saves, carrying capacity, extra languages, henchmen rules, etc. The move to 'you really want an 18-20 in your classes' main stat as soon as possible' seems to homogenize characters more than size benefit/penalties ever could.
As for long weapons being good for short combatants, it is true that to certain degree it is good to compensate the reach. But it simply seems absurd that a halfling would be physically able to wield a great sword twice their size.
I agree. It seems absurd to me as well* . But... (I like that word, don't I?) I dipped out of video games around when they made a second nintendo system. However my understanding is that in one of the late-90s Final Fantasy games, there was a protagonist who walked around with an absolutely
bonkers!-sized greatsword. He was human, and it was like 12' long. That's about what a halfling with a human greatsword would be like. It's not
my fantasy, but I can see the merit to it for someone who grew up with that media (and it certainly seems less absurd to me than 3.5's spiked chain or 5e's one-handed-quarterstaff-and-shield-and-doing-back-end-attacks-with-the-polearm-master-feat).
*personally I miss 3.0's specially-sized weapons for smaller races, but I understand that also was a 'unnecessary fiddly bit' scenario
So again, I do not disagree that small size should have some benefits and penalties, but other than trivial things, everything I come up with seems like grand fiddliness, a penalty for the party over penalty for the player, restricting of race-class combos (which I do think is a reasonable goal, considering the modern games' audience), or the like.