If you don't want PCs to play weird races, just do what Gygax did and make humans the most mechanically powerful race. How about Humans don't have stat limits?
Alternatively? Just say "
no".
I say "no" all the time. I have no shortage of players, or campaigns. "No" works just fine.
However, I don't say "no" just to
say "no". I often do so because the campaign I want to run is something I do not want to be defined by the name of the Adventure -- but principally by the nature of the PC party and who they are. Thematic approches to the PC party
makes the adventure about the PCs, not about the lands they are in, the foes they will face, or who the BBEG is. That may be the book I have bought, but it isn't the campaign I plan to run. That's something entirely different.
This approach to a campaign works. It works
very well when you take the time and effort to bring it all together. So "no" is about
YES to the narrative theme you are trying to create.
In order to have that sort of narrative theme shine through, you need player buy in. Once you have that, all the rest of this multi-racial murder hobo stuff goes away without a problem - and mechanical bonuses are wholly
irrelevant.