I've never had a problem in Ultima or Haukke Hard. There's plenty time for casting in Ultima and for the Haukke boss you should make a lot of use of sprint, a tool melees can't use. I pretty much carried a first time MNK through that fight last week who couldn't stay alive.

Titan EM has a high learning curve for BLM but you can achieve high DPS if you know where to be when. You don't have to stack as soon as the weight goes off, stand there until you get a fire or thunder proc then move back. Know when the bombs are coming in phase 2 so that after the weights that come before you might already be in place for them if they drop in the right place. Use Scathe, Manawall and Sprint to your advantage. BLM is also highly useful in the fight for the caster LB3, it makes things much smoother in the latter part of the fight.