I would have assumed that under Hard difficulty I would be incapable of repairing the ships, but I can - not sure if it makes sense to not be able to repair them under Easy difficulty
They can be repaired under easy and hard, but not under medium. The reasoning is as follows:
Under easy, you get the spirecraft with no drawbacks, and the AI gets nothing to counterbalance them. This is a purely advantageous faction.
Under medium, you get the spirecraft, but they have some drawbacks (like inability to be repaired). The AI gets nothing to counterbalance them. This is still largely advantageous, but a bit more balanced.
Under hard, you get the spirecraft with no drawbacks
but so does the AI. The AI launches waves including spirecraft, so you'd better have some of your own to handle things. This is completely balanced, if not slightly
disadvantageous.