Thats frankly nonsense.
Why are elves and halflings better archers or throwers? Not because of background but because of their biology simply allowing better hand-eye coordination. Same way as for example Tau in Wh40K. Yes they might not know how to use a bow just because they are born (aka, playing a class with no bow proficiency), but their hand-eye coordination stays. The same way a chimps or gorillas muscle density is way higher than a humans so a small chimp could rival a grown man. You are talking about different races, of course there would be biological differences.
It doesn't matter that your elven slave performed hard labour his entire life. The dexterity is in his genes, the same way as having two eyes and two arms. It doesn't have to develop. What your elf develops is a lot of strength, represented by putting a high score into strength. That is what training represents. But ASI you get just for existing.
Elves are better archers because of tradition. Halflings are
not better throwers in 5e or in... what are we calling the next edition now? D&DO? One? because slings are a simple weapon just about anyone can use, and they didn't give halflings any bonuses to use them.
And honestly, "in their genes" isn't that good an excuse. Humans are better endurance runners than basically every other animal out there. We can outrun cheetahs in a race, simply because we can run for longer than they can. That's in
our genes. But most people don't train to run and therefore are simply not good at it, and average Joe would fall over panting fairly quickly. How far can
you run?
I can manage a fast shuffle for a couple of seconds until I remember there's a reason I own a cane.
The same would happen with elves. An elf who really wants to train at being graceful will be very good, and that would be represented by them putting their highest stat in Dex, making an "Acrobat" or "Dancer" background, and taking some Dex-based skills to support that. But average elf is probably not going to do that. Average elf is going to be doing whatever elves do all day, like frolicking in the woods, or painting murals.
Elsewhere, you write:
1. People somehow thinking that different fictional races being different is somehow racist (see @Faolyn's post). Which strangely only seems to be a problem in fantasy, not in scifi. I haven't heard any complains about Vulcans.
That's because SF tries to be at least a
little bit realistic. There's in-setting reasons for Vulcans being strong: their planet is higher gravity, and they supposedly have much denser muscles than humans, and I'm pretty sure that they have a better pulmonary system, all of which are used to explain their high strength. Likewise, in real life, chimps literally have different types of muscles (more fast-twitch muscle fibers) than humans do which enhances their strength (but makes them tire out more easily).
In fantasy, you don't get that. You get
maaagic. You get literary tradition determining what races are like, but literary tradition changes from time to time and so do interpretations of D&D races. Which is why, for instance, halflings used to get bonuses to saves against magic and half-orcs were built to be assassins, not barbarians. It's also why you can handwave things like a loxodon--a literally 8-foot-tall elephant-person--being no stronger than an elf (neither get Strength bonuses in 5e), or a 4'5" dwarf being as strong as a 7-foot goliath (both get a +2 Strength).
not being a big part of fantasy, but the basic idea of how breeding works should be considered. (Like someone domesticated horses and dogs IN your world so I think it fair to say people can assume that trait breeding works most but not all times.
