That’s actually pretty useful.
Weight change on demand alone is useful af. If they can strengthen their jump, that just free perma jump slam.
Sheath, weight null, unsheathes, weight increase, slam/chop.
Depending on how cheating the magic is (and if inventory bag is a thing), they could just attach all their gear & items on the weapon as accessories. Think of those ring on Chinese Dao, really fancy Western guard handle, charm/amulet that sometimes hang on end of sword handle, ect.