The rationale I came up with for my Star Trek Timeline* is that Valeris was the first Vulcan to graduate at the top of her class at Starfleet Academy's command school, which fits well with her drive and ambition, IMO. I figure that most Vulcans wouldn't be too interested in command (as we saw with Spock on TOS).
*Valeris' mention is in the "2289-2299" section, towards the end of the timeline.
That makes a lot of sense.
One thought that I had is that the specific "top of the class" could be based on something of comprimise negociated between the four founding races that each race contributed a number of points to. For instance:
Vulcans insist that they demonstrate exceptional academics, including a good grasp of logic.
Andorians insist that they are physically fit and demonstrate (branch appropriate) grasp of military principles.
Tellarities insist that they are good debaters and don't accept something "must be true".
Humans (and Alpha Centaurans) value role-specific excellence and a sense of adventure.
Humans generally do better because a human can be all these things (though many aren't), whereas a Vulcan could easily satisfy the first and last categories, but might struggle to excel in the Andorian and Tellarite ones.
YMMV.