The mind blade is split so many times that it has to be thin bits that form the panoply. This lends itself to not being solid enough for blunt damage. Additionally, it's limiting factor to forbid blunt damage as way to keep it from being too potent - there is a DR type that they have a built in weakness to overcome. The psychic armory is potent - sacrifices need to be made to keep it from being too strong. This is a small handicap. Also that video would totally be piercing damage
-X