The flaw in your logic is that you assume that all planets have the same number of inhabitants. You also assume that every Federation citizen has a proclivity to join Starfleet. If you look at 21st century Earth, you find that not all nation-states have an equal number of citizens. Some counties are more introverted as far as interpersonal and international relations go.. I think there was even an article saying how the most common "face" on Earth today is male Han Chinese.
My point is that it is entirely reasonable for some species (like the Vulcans, Betazoids, Saurians) to be more likely to stay on the homeworld, while others(Humans, Andorians, Bajorans, Bolians after early TNG, and Trill after TNG), are more adveturous.
And the flaw there is that with over 150 planets and non-human races like the Andorians (I'd say especially Andorians), Bajorans, Bolians, Trill you mentioned it's over 50% humans, sometimes far more than that.
Especially officers are more likely to be humans, particularly captains.
Are those who actually join Starfleet less likely to get to the higher ranks because humans are "superior" officers?
And why is it that of those humans such a ridiclously high percentage is anglophone?
Does what we saw in the shows accurately represent how Starfleet is structured, with the humans at the top, Americans at the very top (remember Picard was the only non-American lead character of any Trek show), while most other species are there to serve as redshirts, or was this simply due to the imcompetence of the authors?
I think the two (more humans than non-humans, more Anglophones than others) are symptoms of the same problem.
Also how likely is it that the populaton of one in over 150 member planets would be the only one to join Starfleet in such large numbers?
Even if we assume humans have a higher tendency to breed like rabbits and populate colonies and also a higher one to go to Starfleet while allthe others are less reproductive and also less interested in joining Starfleet it's quite a stretch that this would counter a factor of 150:1.