Metal smashes crystal, Draemar can learn magic but wouldn't be as good, and there are plenty of techniques in fiction for preventing a psychic from reading your mind that, while the man on the street wouldn't know, I'm sure would be developed for anyone who deals in a diplomatic or combat context with the Shardminds.
Also, they live in a tower and hardly ever travel in group of more than one.
I think I made this same argument about Dryad Miracleing her races new abilities: It does not, in practical purposes, matter what or how many powers a race has. You can work out ways that make sense, in universe, to counter them.
Hey son, wanna' learn how ta' make witch balls?