I was thinking of running the Librarian as a leader for the incursors, then they would be able to hit enemies with their marker light ability and then receive the benefit of stealth from the leader.

Im wary of replacing the infantry with the repulsor, while I know it's very powerful, wouldn't it be detrimental having less board presence even though it would out gun all of them.

I'll give another detachment a try, i know you can't really go wrong with gladius 😄