A frigate is roughly comparable to a T2 tank on cost and HP, about 2/3 the DPS but with more range, and is much faster (very arguably the better unit due to speed + range). The same is true of destroyer vs T3 siege assault bot except that the destroyer is more expensive with much longer range.
In other words, these units are not at the correct tech level.
Wacky, wacky balance idea: push the whole of navy up a tech level by requiring a T2 engineer to build the first shipyard (effectively, we get T2, T3 and T4 shipyards).
Problem 1: UEF and Cybran have no T1 floaty units (besides engineers). New units needed, either from a "small boats factory" or (more likely) T1 land hover.
Problem 2: it wrecks navy balance on most popular navy maps since frigs and destros take longer to get into action. But maybe not as badly as it first appears since their high cost.
Anecdotal: expansion already happens before building T1 navy. Fast T2 air is common on navy maps, so this probably doesn't have a major impact on big navy maps (Setons, Glaciers).
Problem 3: a few weird maps. Saskiya has a water start which becomes untenable without a T1 navy factory (no big loss, people already complain about that). TAG Craftious lets early frigs get major damage in (IMO delaying that is a balance fix).
Problem 4: air is already strong vs navy; this makes it stronger.
Obviously this is a wacky idea, but it's a fun thought experiment, especially considering how imbalanced navy vs land is now.
Probably would have a whole host of balance repercussions:
- Leaves obvious gaps in T1 amphibious capabilities (already Aurora and Zthuee can be imbalanced here, but it's even more obvious without T1 frigs)
- You play Setons and go T2 air. Opponent builds T2 land and sends riptides or blazes before you get navy built. At least you have the air advantage. Hope you aren't vs Phim who have hover flak.
- As a T2 unit the frigate might want a small buff to damage and range (but at a higher cost)
- Not obvious what role subs have in this: but probably not much different than where they are now since they are anti-navy units.