For me, most of the fun of designing my ships is that I can make up an objective and play with different combinations of parts to see how well I can accomplish that objective. It allows for emergent gameplay and creates some really interesting strategic decisions. I can't just have a big fleet of all top-of-the-line models. I'll either need to produce fewer but higher quality ships and be really careful with them, or compromise and use some older components to keep the production and maintenance costs down.
Removing the ship design aspect, and the tactical control from battles, really locks in play styles for species. There's flexibility, but (to continue with the StarCraft example) it's more a matter of using a specific build and successfully identifying what builds your opponents are using. What makes this work is that the game is really tightly balanced. In a 4x game, the balance seems like it would be even trickier because each faction will have a broader set of variables than just a unit list. Plus, a StarCraft match is ~45 minutes at the outside. A 4x game might play out over weeks. The "locked in" feeling might be worse if you're stuck with it for longer.
What might sell me on it is removing nearly all of the tactical portions of the game and replacing them with a good set of strategic considerations. If instead of worrying about individual battles I have to worry about fronts, supply lines, reinforcements, and so on, there could easily be enough to keep me engaged without worrying about individual ship-to-ship combat. And even if my fleet had certain predilections that were hard to get around they would mostly influence what strategic objectives I would pursue. Using my ships for something they aren't well suited to would have to be worth the risk. I'd have to really want that objective.
I'm reminded of the differences between a JRPG, like Final Fantasy, a tactical RPG, like Final Fantasy Tactics, and an "SRPG", like the SNES Battle Ogre or Soul Nomad. In the SRPG's there's little or nothing you can do to influence a given battle, but you can try to control factors like where battles take place, when, and the specific composition of your squads. It felt weird to me at first, losing the direct control over battles, but I really enjoyed the newer strategic elements.
As for games similar to what you're describing, maybe Sins of a Solar Empire? It's not quite a 4x, but it's 4x-ish.