BLM is less than 100 DPS below RDM in Susano. It beats SMN by 200 DPS.
BLM is 200 DPS below RDM in Lakshmi. It beats SMN by 100 DPS.
So, on average, BLM is 150 DPS inbetween RDM and SMN regarding caster DPS. While it's not "the best", it's still completly viable. SMN, on the other hand, is not.

SAM is completly overpowered, don't compare BLM to it. In fact, don't compare anything to it. SAM is in its own category.

Though I do agree that RDM grants too much DPS for the skill floor and ceiling it has, while also having very potent healing abilities and raise. It's also a job which doesn't punish failure that much.
Tuning it down a bit is all the caster balance needs. SMN needs quite a buff too. But BLM is probably at the right spot already.