Anyway, I think when it comes to grappling one-size category difference should impose advantage/disadvantage. Skill can make up a lot for that, and it should only be imposed on "direct contests". By that I mean STR vs. STR, not STR vs DEX. You could actually have it go the
other direction for STR vs. DEX, so a human trying to grapple a halfling (who uses DEX) might have disadvantage on the attempt. Any parent trying to catch a young child running around can probably attest to that.
At a certain point, the amount you gain in fidelity to realism is offset by the fidgetiness of the rules. 5e definitely errors on the side of simplification and streamlining.
What it really comes down to IMO, for racial stat adjustments, is the following:
A. Mechanical. This allows for more of a choice point of differentiation. I happen to both agree and disagree with Defcon on this particular point; I think that people tend to overvalue a +1; but I disagree with Defcon that is meaningless. +1 might not mean a lot with a d20, but in a Bounded Accuracy, +1s are harder to come by, and you are scrounging for each +1 that you can get. Essentially, that whole argument is the "Dude, don't even worry optimizing" argument, except for racial stat bonuses only. It only works if you don't worry about it. Which ... I mean, there are optimizers that play the game.
So while there are some that might be, "Yay, now I can play any race I want and it doesn't matter," there are other that prefer finding particular combos, because of ... reasons I guess.
B. Roleplay. These bonuses reify the standard tropes of D&D and allow players to either revel in them (my Goliath is STRONG!) or play against them (my goliath was cast out for being weaker ...). Mechanics and RP can build on each other.
Again, there are those who would say that we don't need this- these have already been established over years. I don't think that's a great argument. We always have new players, and this combination of mechanics/RP that feeds on each other isn't something they'd necessarily know.
C. Tradition. Ugh. This is the weakest argument, by far. Nevertheless, D&D has traditionally used, for chargen, the Race/Class differentiation to create characters. Given that this has been a rich field that D&D has mined for chargen (which I'm not that into, but some people are really really into) I think a good deal of thought has to be given before changing it. It's like the "six abilities." Sure, if the system was designed from scratch today, it would probably be different. But you need to have both a compelling reason to move away from the old system, as well as a better system to replace it.
Anyway, that's why I would be in favor of keeping "standard" bonuses in race descriptions, and then adding a general "variant race" rule that allows for floating bonuses or the like.