Caster LB shouldn't change. Ranged is the one with an issue as it's weaker and being a line AoE doesn't provide any meaningful advantage. I think the simplest way to help it fill its niche would be to change it from a line AoE to a cone. The far end of the cone would be bigger than caster AoE to make up for the reduced damage. Such a wide cone would be desirable in situations where you need to hit spaced out enemies, like the keys in O10. I also like the idea of adding a support function to it. Keep the low damage compared to other LB's, but then add a free party wide refresh, palisade, or both on top of the damage effect.

I'm not sure about having a DoT LB though, as it would need to do more damage than the other LB's, but in doing so would make the other LB's less desirable unless the DoT was stretched out over a really long time perhaps? DPS LB is all about how much total damage is done. It doesn't matter if it's all at once or over time, as long as it makes the fight shorter.