Eight or nine frames of bees and not as many in the super sounds like they're stretched out and would be better off in one box, in which case nest humidity & temperature would be higher, bees' work would be reduced, and what work they did would be done more efficiently.
Do not worry that one National BB will not maintain a colony during winter: it will. Trick is to get the colony packed in.
You have a medium colony, but if you were to remove the super and continue to feed, the compact workforce would work better at getting and storing it.
Is the crownboard closed & insulated?