It's the sort of game I've been wanting for a long time, a (simple but functional) 4x where you design your own units
The design process is simple enough to be accessible but complex enough to involve meaningful tradeoffs and compromises. Armor makes a ship sturdier but slower, heavier, and more expensive. Big guns can inflict monstrous damage at long range but they are likewise heavy and expensive and eat a lot of ammo, which means more ammo storage, which takes up space and can explode if hit. Soldiers have to move around the ship to do things like fuel engines, put out fires, and reload cannons, so you have to keep traffic flow in mind and try to avoid situations where e.g. a single destroyed corridor effectively makes an entire section inaccessible.
Pictured above is my latest design, the Dreadnought, a monster of a ship with four heavy gun turrets and a thick coating of steel armor. It costs a fortune and moves like continental drift, but it's very good at what it does (dishing out and taking a whole lot of damage).
Have you tried Cosmoteer? No 4x campaign (it's basically one guy making his dream game, so development is slow). But you do design ships from scratch. It's like Dwarf Fortress if the fortresses could fly. Some weapons are modular. There's a lot of design tricks people have cooked up. Competitive multi-player is a thing if you're into that.
I have! I didn't end up enjoying it because I found the difficulty curve too unforgiving. I wound up in situations where I had to keep doing repeating missions with pitifully small rewards to be able to progress.
Ah yeah. The dev has mentioned he wants to completely overhaul the campaign to be more like Faster Than Light, Alpha Centauri, or a full-blown RPG, but it's a long ways off since he hasn't even added aliens or proper docking/carriers yet.