I am a BLM and a SCH and I certainly do not outnuke myself on SCH versus my BLM. Inside of Aby no SCH won't come close enough without the intelligent use of immanence to create SCs (and then a BLm can just MB on the SCs to increase the own dmg yet again). But trying to built SCs has it's limitation that most melees will just WS in between more often than not.
If MP isn't an issue as BLM, casting speed is even faster than a SCHs and enmity can be wiped out (only every 10 minutes though) a SCH cannot outnuke a BLM if they have even atma effects. But outnuking is just not what a SCHs is for. I don't want to outnuke my BLM. I want to be able to nuke hard enough to be worthwhile, while supporting the party. Supporting it by using weather spells to increase BLMs dmg, building SC or turn around and buff melees with whatever.

SE should just start lifting the need of addendum:black for T4s.