The whole family of mustalids are fantastic at hunting when they elect to do so. Fishers routinely feed on porcupines and a wolverine (which weigh ~30lb vs the marten's 3lbs) once killed a polar bear, both were captive animals in a zoo. Also if you look it up there are videos of 7 oz weasels taking down rabbits much larger than them.

We're lucky there aren't any 90lb mustalids.