This is sort of semantics but it really needs to be pointed out again, since it can lead to people getting on the wrong track for damage calculations: dual cast spells still trigger the GCD. It's not like you're getting free spells in there, its just the difference of them hitting at the start or end of the gcd. Jolt+ VerAero/Thunder is NOT a 480 pot attack. That combo averages to 240pot over two gcds.
Dual cast is pretty convenient in a few ways but the increase in dps from dual cast only comes from verthunder/aero having hard-cast times that are longer than the GCD.


It really remains to be seen exactly how good the RDM dps is but I'm pretty sure they didn't drop something OP on us with this one. Like, I don't know the exact average potency but Blackmage is chucking lots of FireIV at 260+the Astral Fire Buff. RDM's average is about 270.
BLM vs. RDM comes down to this:
BLM's main rotation is certainly higher damage (fireIV is a good bit more damage than RDM's "rotational" spells)
BLM's burst phase is lower than RDM's (Foul is 650, they only get it once per 30sec, RDM's melee averages 380 over its 4gcd)
BLM has a bit of a lull-phase during umbral ice.

So RDM can "catch up" to the BLM's more steady high damage through its ability to burst with the melee combo.