The Sword was neither heavy, nor capable of doing anything other than being a sword and bringing inanimate objects to life in the movie. --- Screw the rules, I have green hair! Broly's power is NOT maximum.
Nor does he have a bum leg, though he does rest the sword on his shoulder at one point in the movie. I suspect he carries it like that because a) he did briefly in the film and b) the sword is larger than standard lego swords and would probably have clipping issues if he held it normally. --- "I'm going to go do British things, like drink cups of tea and eat bangers and mash, that sort of thing...because I'm British"