See, tho, there WAS a reason we did so well in Starfleet. Because humans were part of it's founding mission to poke at anything and everything we find to gain even greater understanding of the galaxy, ourselves, and science in general. There was one thing we had that Vulcans truly lacked, something they gave up when they embraced the teachings of Surak. Naked ambition.
We humans accomplish more faster than any other species simply due to our psychological drive to know absolutely fucking everything and our inability to accept that maybe we can't. Vulcans don't find exploration for it's own sake practical, rather they tried to approach it from a pragmatic standpoint. We humans will land on a resource barren, uninhabitable world just to see what the fuck might possibly be on it. Vulcans, with their lifespans and logic, have no problem undertaking a 500 year project to advance between warp 1 and warp 2, but a human scientist wants to goddamn see this shit right the fuck now before he dies.
It took the Vulcans 1,000 years to rebuild their technology after their last major war and discover Warp drive. Humans managed it in less than a century. Not to mention that of all the species in Trek, they find us humans the least predictable.
Klingons, Cardassians, Romulans, Ferengi, all the other races can be reasonably expected to act much the same way. But humans are so insanely varied that the Vulcans find it almost impossible to actually predict what any given human might say or do more than any other race. We're constantly surprising them even after a century of experience with us.
Not to mention we breed like fucking rabbits compared to Vulcans and expand out of necessity faster than any other species, colonizing shitloads of planets. Kirk stated we (the federation) had spread across thousands, thought Picard stated the Federation was spread across 150 "member" planets. But given Kirk's statements, and the fact that the Vulcans only managed to colonize a canon 26 planets despite their substantial advantages both technological and in time, I'd say humanity has spread across a substantial number of planets.
And don't forget, we humans are willing to take risks that Vulcans aren't because of out impulsiveness, our emotions/ Vulcans would be content to take the safer route even if it was the slower one. Humans don't deal with that pussy shit. Damn the torpedoes, full speed ahead! Might as well be our motto as a species.
Basically we outperform them because we outnumber them, and we're willing to do things they aren't to get results right the fuck now.