[wizofaus]

Plenty of people I know handwrite faster than they can type! And have they tested those using shorthand?

What I could believe is that our brains might be better at remembering the sorts of movements our hands make while handwriting (essentially using your wrist and elbow) vs those made while typing (fingers only), perhaps because the former are closer to the act of manipulating the physical environment in ways that might needed for survival (gathering food etc.) and because you're physically tracing out a desired path in 2d space, though it seems tenuous at best.