The imperials don't have anything like droids (or a similar flexible card) that is essentially a free upgrade slot on a handful of ships with a wide variety of options.
I wonder sometimes if giving Saber/Black/Royal Guard pilots EPSs wasn't an attempt to balance that out, since the green squadron pilot (only rebel generic above ps 2 from wave 1+2 without a crew or droid slot) is the only generic with a EPS but as EPSs started growing in power they decided to just start restricting their availability to the named pilots