I think the number 1 reason comes down to just 1 unit :
UEF destroyer : 274 DPS, 60 range. 30 torpedo DPS.
Aeon Destroyer : 212 DPS, 80 range, 106 torpedo DPS.
Cybran Destroyer : 230 DPS, 100 torpedo DPS, 80 range.
Seraphim Destroyer : 195 DPS, 60 range, but 160 torpedo DPS,
I already knew the range disadvantage of the UEF destroyer really hurt it, but the torpedo DPS difference is what really gets it slaughtered. Most destroyer fights have at least some shots fired within torpedo range, or the enemy has subs!
This is not even a question : just from the stats, UEF t2 navy is going to get slaughtered on any navy map. Couple this to the fact that Aeon navy now has shields that are better (in the form of the cheap t2 land shields), cybran gets an extra gun on their cruisers with for an even more insane DPS advantage, and that 160 torp dps means that seraphim destroyers are also going to win against uef t2!
Yes, there's coopers, but that's another 900 mass for a 1750 HP ship for 96.97 torp dps, which is an extra ship to micro, more rolloff time, more mass, and the enemy factions get 100 torp dps on their destroyers for free!
Where UEF would shine was at T3. UEF navy dominates at t3 because it's 540 DPS battlecruiser will pwn far more than it's mass in destroyers, and they get the best battleship.
But the new patch makes the barrier to reach T3 navy enormous : 7120 mass. This means in 1v1s, the UEF player has already lost navy, and has either lost his shipyards or is about to lose them, by the time he has enough t3 mexes to spare 7k mass. Conclusion : either the t3 navy cost needs to be fixed, or UEF t2 ships need to be buffed.