I've never felt I strictly needed the Aleph models to give my opponent a challenge. The Aleph borrows are -very- good, for the most part, but NCA and SAA get along just fine without. The Aleph borrows DO increase the variety of things those Sectorials can make their opponent worry about, which in that sense, yes, the Sectorials are weaker if they didn't have Aleph models. They're still not strictly required to be in your list to do consistently. The Naga is the closest I would get to saying "absolutely necessary". They're hard to leave at home.