Here are my thoughts. I of course think that all characters of all bloods should feel like they can be useful, in roughly the same proportions. There shouldn't be one that really dominates, but I think you might be going about that the wrong way. I don't think it is worth it to lose variety in favor of closing off every bit of potential for abuse. We're all friends here, after all, and we can deal with those issues individually. 

I think it might be possible to "over-balance." To think about every detail of what every blood can do that you drive yourself crazy. Personally, I like the potent magic. I like the idea that we have this great potential. When I see a fight between a master aeromancer and a master geomancer, I'd like to see a mage bringing down the sky to meet the earth rising up against him. I'd like to see the forest turning against a pyromancer who is scorching the earth hot enough to melt the rocks as they try to get to the herbamancer. When we get all of these master bloods fighting with and against each other, I'd like it so seem like reality is tearing itself apart, because I think that it would make the RP all the more interesting. I like being able to be creative with my abilities, and it really does not matter how much power our characters can potentially have, because the enemy has mageblood too. They will have all the same powers and abilities as us, if not more. 

Instead of trying to nerf everything into balance, I say "balance-up." Make sure that every mageblood has some kind of strong defense against other magebloods, some way to absorb or avoid damage, so that master level fights don't end in two seconds. I haven't had time to think in depth about every single blood, but I'm certainly willing to. If we work together, I think we can make sure that each blood has a compelling and potent defense against each of the others. That would certainly be easier than trying to rebalance everything.