Having both meister and wielder mandatory seems like a stroke of genius to me.  While having two players coordinate each half of a pair is good in theory, it would involve way too much coordination for many things, mostly fights.  That begs not only the question of players being left out, but players dropping out being utterly blueballed.  Plus, being able to make a duo guarantees that we'll always have something to write about.  Two characters bound to interact together means nobody will lack material.  Plus, it opens the way for great pair dynamics.