Yes, at level 16, a Bonded Summoner may bind a CR 16 creature. The Legion Magus may change what type of creature is bonded to it any time it gains a level in the class. I'll add the to the description. And it should be noted that it can use Draconic Auras with their Major Aura bonus, should they learn them. Perhaps I'll give them a Draconic aura every few bonus levels for free.