Main issue is, and the reason a passive raise tax is a thing, is if RDM and BLM do comparable damage but RDM brings a safety net, there is no incentive to bring BLM. On the opposite end, you have no reason to bring Red Mage if its damage is so low that after learning the fight the guy you have playing it needs to swap to BLM and partially relearn the fight anyway.

The issue of giving DPS non-damage "support" comes multiple times. 1: this game is so focused on dps that even healers and tanks are hard focused on it. 2: if dps is balanced against support instead of other support options (ie: if RDM brought raise 1/min but BLM brought reraise 1/90sec) and that was the balance or choice? Sure that's a variety thats ok. But "9000 dps but no raise vs 8000 dps but raise" is a recipe for fracturing an entire role's balance.