When it comes to ship numbers and the types of ships the GTVA uses, consider two things:
1.) After the Great War, most of the Vasudan shipyards were probably destroyed by the Shivans. Most of the Terran shipyards were located in Sol, which of course was cut off. The Vasudans were able to rebuild much faster than the Terrans, sp when FS2 starts they have more shipyards then the Terrans did, so their fleet was almost completely modern (unlike the Terrans, whose fleets had lots of Great War leftovers)
2.) They also have something called "a budget" to worry about. The Vasudan economy was much better than the Terran economy, so they could afford to wield many of these shiny new warships. Why else do we see so many Sobeks in the main campaign, but not as many Deimos's? Or just looking at the cruiser types that we see, the Vasudans always seem to have brand new Mentu cruisers when the Terrans frequently use refitted Great War era designs.