BLM just requires more skill to play in terms of mobility. You have to pre-position and know mechanics a lot better than pretty much the rest of the party. That said, they still have great mobility, especially outside of savage where they can be a lot more care free with their instant skills and stepping out of leylines isn't the end of the world because...well...its not savage so it doesn't really matter lol.

I can't comment on this savage tier since I'm back to playing melee and gave up the caster spot to one of my friends in our static,. but honestly last tier I never really had any problems placing ley lines down and being able to stand it it basically the entire time. You just need to know when and where to place it.

Honestly, BLM is pretty much perfectly designed and shouldn't be messed with too much.