The Hecate is a significantly more dangerous ship than the Orion purely because its larger air wing gives it much better striking power, and lets it use that striking power without putting itself in the line of fire. If a Hecate finds itself using its anti-capital beams, someone somewhere has screwed up.
The new line of Vasudan ships is not significantly more or less modern than Terran TEI ships. However, their Capella-era fleet has received more upgrades than the Terran one. The Terrans are slowly replacing their Capella-era fleet with new ships, while the Vasudans are upgrading theirs to more modern standards. Overall, it's a more advanced fleet, but the top-end of that fleet isn't higher. They just upgraded most of the stuff on the bottom end.
Remember that the biggest reasonwhy Terran beams were weaker than Vasudan ones in FS2 is because Terran beams were built for backwards compatibility, while Vasudan beams were not. It's why the Terrans could put 3 BGreens and 3 TerSlash on an Orion while the Typhon had issues with 2 BVas.
Considering that the GTA destroyer fleet only has six "modern" combatants by the end of BP2 Act IV
Nine. 4 Erebus (Atreus, Orestes, Agamemnon, Menelaus, +1 nearing completion), 5 Titans (Imperieuse, Temeraire, Implacable, Conquerant, Pallas).