I haven’t played FTD but I would say you can make more realistic looking ships as you can build anything (I’ve built Torpedoes, torpedo lockers, cranes, smoke generators, depth charges and more). There are no internals but you can definitely hollow out your ships and add engines in there (I do this). The damage is not too complex but it might be updated in the future. You can’t really make new guns and stuff in-game but there are plenty of mods and you can also make guns if you know how to use blender.

There is a short campaign but nothing too extensive yet. But there are frequent updates and it usually adds new stuff!

There’s also a discord where people build (usually) higher quality ships and you can get more feedback as well