How powerful are
the Vulcans and Andorians during the 22nd century? They're apparently a match for each other, but what does that mean? The Vulcans had warp drive thousands of years before humanity, probably before the Klingons and maybe the Andorians, too. Why didn't they take over the entire Alpha Quadrant long before the rest of the future Federation members, and end up with a Vulcan Empire matching wits against the strength of the Klingon Empire?
Apparently Vulcans are homebodies. Sure, they have a couple of off-world colonies, though P'Jem was a monitoring station/meditation retreat, so how much "power" does that add to the Vulcans? And the Andorians - how big was their
"empire"? Just big enough to match the Vulcans, apparently....
Humans are the glue that holds the Federation together, and they do it by convincing their "compatriots" that without them
, anarchy would reign! At least being in a nominally equal relationship with the true Human Overlords of the Federation is better than being explicitly inferior in the Klingon Empire!