Nursing/pumping that side would eventually increase the supply, but not necessarily be even with the other breast. No guarantee that would increase the size though

I definitely would not try to even them up with cabbage leaves (though I think you were joking here, just in case!), you might dry up more of your supply than you want and then your baby wouldn't be getting enough milk until it reestablishes.
It is common to have one breast that produces more than the other and ends up larger than the other and it isn't a concern, but yes it can be a annoying when the size difference is significant. My right breast is normally 1/2 cup size smaller than my left, but now it is at least a full cup size smaller since it produces a lot less. It is from baby preference though probably because my nipple is somewhat flat on that side.