Yes, there may be more dwarven fighters than elven fighters, but -- if you have an elf fighter -- that character should be able to hit the opponent just as well as the more numerous dwarven fighter allies. Similarly, dwarven thieves might be rarer than halfling thieves, but a lower dex cap shouldn't limit the dwarven character.
Yes, well, if they can do the job just as well, why are there fewer of one than of the other.
In addition, "able to hit the opponent just as well" does not necessarily equate to, "has the same strength". For example, if the elf has the 5e equivalent of Weapon Finesse, that elf may hit as well, without being as strong.
Plus, there's more to being a fighter than hitting. There's also doing damage. There's also soaking damage. There's also not getting hit in the first place.
I don't mind much if some races just aren't suited for some classes. Maybe halflings don't make great front-line fighters. I'm okay with that. I prefer the Star Trek approach - IDIC: Infinite Diversity in Infinite Combinations. Celebrate the variations of the universe, rather than attempt to iron out all the wrinkles.