So what gave Spock his great physical strength would be his half Vulcan heritage and up-bringing.
...I wonder whether Spock had to develop exceptionally great strength in order to ward off all those bullies who felt it logical to try and unscrew his halfbreed head?
It might also be that half-humans are much stronger than either humans or Vulcans, thanks to some sort of "hybrid vigor". The fact that the T'Kumbra
baseball/wrestling team was superior to the DS9 team could have been due to a single one of the Vulcans being stronger than Sisko, as quoted (for whatever reason), and the rest of the lot simply being much more accurate batters and pitchers than any of the Niners...
Of course, realistically, aliens wouldn't be humanoid at all. But it doesn't pay to approach these as black-and-white questions. Yes, it's a work of fiction, but it's one that's generally made at least something of an effort to justify its conceits.
Then again, Trek did justify the humanoid aliens by claiming they were all engineered to be that way. This sort of preempts all "realistic" concerns: if the environment in which the humanoids grew had an effect on how they grew, they would probably diverge from the great plan of the engineers. Unless the environments were also carefully engineered, so that all the life-bearing planets would have Earth-normal pull, and all planets with different pull would somehow be secured against bearing life.