Hmm. I'm only a level 20 conjurer, but I used to be in high-end raiding in WoW, here's some of my thoughts.

1. Battle Raise without a long cooldown/lockout would simply be OP, every boss fight would be easy and it doesn't punish players for being bad.

2. Different ranks also has different mana costs, hence you need to choose spells accordingly.

3. Of course if you go crazy with spells you're going to go OOM, that's the entire point.

4. Yeah, the spells do lack creativity.

5. I doubt WHMs are expected to do DPS in fights, and even if they are, the DPS from Aero is minuscule, hence the mana cost is only relevant in a solo setting, in which case mana isn't an issue anyway.