The reasoning behind this change wasn't so much to make the fight easier, but rather because the mechanic just wasn't really playing out the way we wanted it to.
Do you mind indulging the intent of that mechanic versus the actual outcome of it?
Healing Forum MVP
The intent of the mechanic was indeed to require the raid to take turns cycling through the Breadths of Frost to reset their Superheated stacks, and to destroy the Breadth if too many people tried to camp in it at once. As it turned out, players discovered that a very, very precise triangle formation allowed three independent clumps to coexist inside the Breadth without triggering Geyser. All of the initial Heroic Ragnaros kills used this tactic and it became the standard way of doing the fight.
We could have increased the detection radius that triggered Geyser, but in general we try to avoid enacting changes that make an encounter more difficult once that fight has already been defeated. Doing so creates a frustrating experience for players who have to relearn something they believed they had mastered. The adjustments to the health and damage of Ragnaros and his minions in September primarily affected the difficulty of phases 1-3 of the encounter; at that time, we also decided that Magma Geyser should be removed from phase 4, but the change was not one that could be made in a straightforward way via hotfix, so it did not take effect until the 4.3 patch.
So basically, yes, it’s a nerf, but it’s because we weren’t happy with the mechanic and the only two solutions for fixing that were to either make the fight harder or to make it easier. And, as stated above, we try to avoid making fights harder once they’ve gone live.
Despite some of the insinuations in this thread, the change isn’t remotely going to let a guild that hasn’t mastered the encounter just walk in and defeat it.