If people using fighters as a missile sponge is unintended and unwanted, the easy way to solve that is to have rebuilding extra ships beyond one cost a tiny amount of scrap. (To never leave a player totally defenseless.)
I like the idea of shield drones, though, being used intentionally as a missile sponge. I wouldn't want them to take much damage - fighters and drones seem to soak 100 HP now, and any shield drone should form up into wall dense enough to be difficult to penetrate, but I don't think they should absorb more than 10 or 20 HP. There are few weapons that shouldn't destroy them with one hit.
Beefing up fighters would help their usefulness, I think. Give bolter and plasma fighters 200 or 250 HP, then see how they shake out in a simulated battle or five. Missile fighters already seem decently balanced, I think, though I haven't tested them extensively.
I hate suggesting nerfs, but bolter fighters may need them. My first thought is build rate. Drone-heavy builds often get underwhelming fast when you hit a fleet with good fighter control. Once they've winnowed down your drones numbers, there is no coming back from that unless you can finish the battle conventionally, or run away to rebuild your drone fleet in your hangar. If those aren't possible, you have to jump out of the sector to rebuild yoru drone fleet.
