One thing to bear in mind is that this is only the first wave of empires to appear in the game; depending on how deep into the wider SFU that Mongoose decides to go, there are many other fleets out there to be considered as the game expands.
Indeed, just as the five starter fleets in
ACtA:NA had a more similar technology base than they each would have with, say, the Vau (set for
Fleets of the Fading Suns), the five full fleets currently in
ACtA:SF were the first to be created for
SFB (and to be converted to both
FC and
Starmada) back in the day; the further out into the SFU you go, the more new dynamics and concepts start being built into this foundation.
In the Alpha Octant, the local empire with the biggest and bulkiest hulls per ship class is the
Inter-Stellar Concordium; their Star Cruiser is larger (and more expensive) than those of the "insane empires" they set out to pacify. Plus, their fleets are renowned for the Echelon formations they adopt, in which gunlines of plasma-armed frigates or destroyers screen larger second- and third-line capital ships armed with longe-range direct-fire plasmatic pulsar devices.
But even they break a sweat once the extra-galactic
Andromedans show up...
(Though I would imagine those two might have to wait until we get the likes of the
Neo-Tholians and
Seltorians, or the
Lyrans and
Hydrans, to get settled in before they have their turn.)
So, if you're not sure about the current batch of empires, there are more on the way which might make be worth keeping an eye out for.