I dunno to me, it works well ...
I see +1 as being better ... and +2 as being exceptionaly better.
Therefore bcs Humans get +1 to everything, they are slightly better in every aspect ... but not exceptional in anything. If that makes any sense.
(Con) Human is Tougher than Elf, but not as Tough as Dwarf ...
(Dex) Human is more Agile than Tiefling, but not as Agile as Elf ...
(Str) Human is Stronger than Elf, but not as Strong as Dwarf ...
(Int) Human is Smarter than Dwarf, but not as Smart as Gnome ...
etc.
Sure, its not so flashy as other racial bonuses ...
But i like this explanation: Humans are major race in most parts of the world, bcs overall they are "better" in everything, even tho if you pick specific aspects, there will allways be some other race that would surpass them.
Interesting point about Half-Orcs tho ...
I still dont understand why cant we change Race for our hirelings.

Lets us play Githyanki as racist as they trully are!