I think letting characters put an extra +1 in a stat of choice makes the system worse because if an 18 is available that becomes the new baseline and a 16 no longer looks good enough. Restricting it to +1 in a stat you don't already have a bonus in sounds better to me.
Personally though I prefer Tasha's system where you can swap an Elf's +2 Dex for +2 Str. I like this because it lets you much more freely choose which race appeals to you rather than being pushed heavily into tropes. Having no cost at all means it can make the races feel less distinct but that's less of an issue when its only one PC who has access to it.
I don't like the Tasha's swap because that does undermine the racial traits. They might as well not exist at all if you can just switch whatever you want.
The 18 vs 16 really has to do with certain races getting that +2. Humans could only start with a 17 even if they got an additional +1 from a feat. Only races that have a +2 could start with 18 and that seems very appropriate. Otherwise that +2 doesn't mean anything. Half-Orcs need to be "stronger" and elves need to be "graceful".
