Holy crap, this scene is about Stevonnie!
Steven’s shield is gem-bound, like most gem weapons, but the sword is terrestrial, because it’s for Connie. And it’s too big for either of them because they’re meant to fight as a fusion.
There’s no better conceptual metaphor for a gem fusion than the pairing of a sword and a shield. And there’s no better visual metaphor for a fusion than literally what we’re looking at right here, THIS SHOULD HAVE BEEN SO OBVIOUS D: