I've always imagined that uglies would have terrible performance in any kind of atmosphere. It seems more plausible to me that one could successfully cannibalize myriad parts from craft and have it operate semi-decently in the bare vacuum of space.
I think that the primary purpose of the R2 unit's head is to act as a backup weapons system. If the X'Ceptor's weapons system gets too badly damaged the R2 unit would magically produce a flammable lubricant vomiter, coat the target in said puke, and then another arm tipped with a mini-rocket would cause the supper slick vomit to violently combust into a flame so tremendously terrible, that in a matter of 2 seconds the targeted craft would slip, land on its dorsal, and have its internals explode out--and all in the vacuum of space.
The Death Star, had it been assaulted by such snub fighters as wickedly equipped as the X'Ceptor, would
not have had a
chance.
