See the SFO presentation linked to by tphuang above. In the BTS stats, VX is lumped in with the 24% “other”. Not sure if that’s because nationwide VX is too small to report or they really are behind AA, DL, WN, and Skywest. No matter how you spin it, AA, DL, WN, pmVX, and Skywest are all within a percent or two of each other at SFO. Of course, DL and AA both have some regional operations which aren’t included in the mainline stats, so they’re a bit bigger than the stats indicate (but not by much, since both use mostly mainline at SFO). And of course, your departures count doesn’t count seats. Apparently AA and DL fly larger planes, on average, to get more capacity with slightly fewer flights.

And saying that AA only serves 8 destinations is of course misleading. Since SFO is VX’s main hub, they pretty much only serve the cities with nonstop service; that is, pmVX can only get you to 25 cities (by your count) total. Whereas with robust service to every hub except the perimeter-restricted DCA, AA serves literally every airport in their network one-stop out of SFO. VX obviously isn’t quite something to sneeze at out of SFO: they’re useful for much of the travel for a lot of people. But (in terms of network alone) they’re not clearly more useful than even AA, let alone UA, for many if any travelers.