they aren't, 'cause sisters are better.
they have better shooting, cause 30pts of marines gives you 1 1/3 hits, but 1.5 with sisters. The jetpackers have equal ws, artificially equal bs (re-rolls), the potential for better morale and combat skill with Acts, and I think they now get withdraw too. space marines don't have squads which take non-heavy special weapons (dominions). They definitely don't get retributionists