That is a good argument to put it on the melee combo, but given how little use that sees, I don't think it would be a good idea. I'm an advocate for adding Verwater/Blizzard into the rotation as mana spenders/converters that you could use in place of Aero/Thunder in the current rotation, which would help with that problem. The conversion rate would be something like spend 7 black mana for 3 white mana for Verwater at 360-400 potency and vice versa for Verblizzard. The potency would be whatever it takes to come close to the melee combo in DPS. I figure they would get the Verstone/Fire proc as well. This would turn the melee combo into something you try to align with raid buffs and personal cooldowns rather than something you always fish for, which the DoT would help facilitate by keeping your mana relatively even in tandem with the spenders. That's the idea I had in mind for it, at least.