It's true that there's at least one all-Vulcan Starfleet ship, and we know that many worlds in the Federation still operate their vessels independent of Starfleet.
It took until Season 3 of 'Discovery,' in fact, for a series to star an alien captain. In fact, despite being a founding member of the Federation, it's stated that there are no Andorians aboard the Enterprise, nor do we see a single Tellarite throughout the entire seven seasons of the series. However, while there are ostensibly a handful of non-humans serving on many Federation ships, we hardly ever see any of them, and it's almost always humans milling around the corridors. 'The Next Generation' had Worf and Troi, for example. Sure, every series has a token alien or two on the bridge.
