Mass regen doesn’t do anything. It does less healing than one spell’s worth of damage. Chain casting it on one group to heal would be the stupidest thing you could do.
The only reason we use it, is to apply beacons, and we cancel it as immediately as we can to cast something better. Its cooldown has limited our healing in casual raids, as we can only cover four groups at at time. So anyone in group five gets left behind.
Every second we’re casting mass regeneration, we’re not actually healing anything. Prepulls have been standing there, spamming it on four groups until the raid is ready to go, and drinking in between. Going through hundreds of waters a night to start a fight with full mana (not an issue, we make our own, just tedious).
If mass regeneration had no cooldown, it would be a 7 second prepull to mark all the groups, and go. Then when beacons are expiring, you have to choose: do you need more dps to heal, or spend ten seconds putting beacons on the entire raid again? Or, do you reapply them a little as you go, in between spells?
Casting mass regeneration is a waste of time in and of itself, so if we keep it on that many groups we’re not doing anything. You also consider how much mana it costs, and there are your drawbacks. You can’t mass regen five or six groups forever.
Getting rid of the cooldown also fixes the problem that haste has introduced. At six seconds, with a 1.5 second GCD, you could cast three instant cast spells before recasting mass regen. Or you could cast an arcane missiles, and one instant cast spell, and waste 0.5 seconds. Or you can cast two arcane blasts, which USED to take five seconds. Add the GCD, and your mass regen is always up. Now, you cast two arcane blasts, and it’s only four seconds. With the GCD, you have to either wait half a second doing nothing before reapplying it, or cast another instant spell, delaying your mass regens. It’s just clunky. So this gives you the freedom to reapply when it fits into your rotation.
And then, if you still feel the need to nerf and hate us, increase the mana cost, lower the healing of beacons, whatever. But let us play.
Also, make the infusion of souls trinket apply to heals, or give us a heal version (this would be awful, as we would want both).
Also, make haste affect arcane missiles. And evocation.
There are so many ways you could make mages happy, while still balancing. The fact that you’re not is a deliberate choice. Don’t hate us, it’s not our fault.