Starfleet is supposedly an exploratory and defense** fleet representing the entire Federation. Yet its command hierarchy is dominated by humans, its headquarters are on Earth, its flagship is a human-dominated vessel and almost all major battles are led by human commanders.

I understand that the Vulcans are not into exploration and Andorians tend to be isolationist. But I'm surprised that none of the many races that make up the Federation seem to mind humans controlling their primary defense fleet, especially given that the Federation is about as cohesive as the UN security council when it comes to political matters.

** Or, in the alternate timeline, a scientific, humanitarian and peacekeeping force.

(A related question, which I came across while checking for possible duplicates asks about non-human Starfleet vessels)