I think the core of the issue is that, the way abilities are given to players, jobs change dramatically as they level. BLM sub 50 and BLM 50+ can almost be called completely separate jobs.

BLM isn't the only job that suffers this, and definitely not the only one that feels stupidly incomplete until level cap or darn near it. So perhaps a good compromise suggestion would be to mire intelligently provide abilities through the leveling experience.