Making it evolve later would make it even more useless.
I do have to say, in addition to this, that B/W really dropped the bomb with evolution levels. Such as Hydreigon. 64? 64? I rarely ever train a Pokemon up to that level, unless it's one that I'm planning on using longterm! Plus, Braviary should have evolved earlier. I'm sorry, but 54 is just too high.