I interpreted the easier to level discussion about which is easier to solo the early levels, in which case I'd say it depends. WHM without a sub is clearly easier than BLM without a sub, but once you can sub WHM to BLM it's much easier.

In any case, BLM isn't too hard to level anyway. The bind and nuke tactic works very well and if you move quickly, you can usually kill it before it can come to you, particularly if you're just fighting a bunch of easy prey, which as far as I'm concerned is the smart way to level.