A friend as SCH and I as BLM were doing limbus King zone for the LS, what can I say, with his potency JA and spell up, he nukes slightly more than I with the same tier IV spell. Mind you, I even got slightly better gears than he does (such as 2 snow rings for me, 2 diamond rings for him). From what he told me, Ebullience and weather give him 30% MAB potency (and Ebullience is 20% potency of total MAB, including 10$ weather, so the number is big). When resistance is not an issue, BLM can't beat that big number of MAB with gears and Job Traits.
I can't touch my BLM nukes on SCH. Using Ebullience (+20% damage) is stupid anyway unless Tabula Rasa is up since Parsimony (-50% MP cost) is so much better.
Correct me if I'm wrong, but I thought that the most you could do with relic WSs was a double Light or Darkness? (Meaning after that you'd need to open the chain from scratch again with a WS that closes no chain)
I think BLM is fine. It's a useful job in plenty of situations. But don't limit yourself and have only 1 job at 75; no job can do everything. Yea it could use a boost, but it's hardly garbage. Elemental staves are insane, and going beyond that is something SE doesn't seem to want to do.
Don't forget DD need good support to do well, give BLM some proper support too.