This is a gameplay and realism nitpick. Feel free to ignore it ๐
The mechanic who repairs a ship should probably be stuck at E until it is repaired. In addition, they should be unable to repair a different ship in your fleet in parallel with the first.
It's pretty typical for me to have multiple ships repairing at once and then I take all the mechanics with me on dives while they repair. This seems too OP? I'd be quite happy to hire even more mechanics.
I do understand the existing wonderfully simple system. You'd need to create a queue of mechanics tasks that get done over time if you wanted something realistic - what a PITA.
Or you could put mechanics on leave while they are repairing something. That would probably require the player to manually chose which mechanics to keep in reserve as ship crew. Sounds complex.