What do you think?
Edit: I forgot to quote the person I was replying to
IMO your salvo sizes on you missile ships are way to small. For anti-ship missiles larger salvos are usually considered above the reload rate of launchers. Consider using size condensation to fit more launchers but be prepared to wait longer. It's usually good practice to have the reload rate slightly faster than the max flight time of the missiles you plan to fire from it so that by the time your missiles hit you ready for more. Launching more missiles at once helps you overwhelm enemy PD.
Your AMM launchers ideally should be able to fire every 5s if your tech allows but 4 AMMs is also not enough for anything really since you will want to launch multiple missiles per enemy missile most of the time.
Your destroyer is about 6k tons and it can fire... 4 shots. For reference, your two gauss cannons can fire as many shots as a single railgun, not only that because of your tracking tech their tracking speed is quite slow too, so on average each destroyer probably wont even be able to shoot a single missile down in final defensive fire. 20 of them? I don't know haven't done the math but it would be a good kill rate regardless - i'd expect more of a 6500 ton vessel (I consider that size a frigate but that is irrelevant).
Your operational range on the destroyer and cruiser are ok but on some binary systems they would need tankers. The range of your battlecruiser is bad and I would try to raise it, however I find it concerning that it can only do 13bn with 20m fuel.
You fleet in general is also pretty slow which is going to be a problem for any beam weapons you try to field. Expect the enemy to be able to outrun you.
Most of these issues boil down to the lack of tech, the ECM 10 and rate of fire 2 gauss weapons are giveaways for this. Your maintenance endurance is really good but it lacks punch and cant reach far without any tankers. I would focus on trying to make faster ships that can reach farther. ECM is also king, good ECM can make your ships unhittable but this works both ways so invest in ECCM as well as ECM.
The only ship here that I think is actually bad is your assault ship - it is way too slow to be useful in any sort of boarding action. I assuming that your troops have boarding capability - if true this means that the boarding ship needs to be 5x as fast as its target in order to avoid casualties to the boarding party. Because of how slow your ship is - most if not all your space marines will die before they even get to board the enemy ship. Use military engines on boarding vessels to make them faster, thankfully you have lots of fuel on this one so it should have ok range.
Alternatively you can have your boarding ship be made to sit in the hangar of a bigger ship that gets it close to the target and then launch a very fast "boarding pod" with your boarding units in it.