Just fyi, blizzard took in exactly two days of data after 5.1 dropped before nerfing the crap out of Fire.
That was also mid-tier, so there was quite a bit of data already that could show Fire doing too much. New tier has pretty much none of that, and with the magnitude of some of the other changes, it's hard to judge how things will pan out.
This isn't really accurate. Before 5.1 went live, several blue posts and at least one tweet from GC said merely that they wanted to tone down Fire burst in PvP, specifically because of alleged multiple shattered Pyros.
As such, they briefly proposed an ill-advised three second cooldown on Pyro. One of the problems with this cooldown is that it would have severely nerfed our mastery, which is a rolling DoT called Ignite. And moreover, ignite was a large part of our main cooldown, Combustion. So at about the same time, they made a PTR change to Combustion, getting rid of the Pyro DoT contribution to Combution and raising Ignite's contribution to Combution from 50% to 100%. One of the blue posters specifically said the intent was to keep Combustion where it was before removing the Pyro DoT contribution.
Meanwhile, they realized how insane the Pyro cooldown was and got rid of it. Then we didn't hear another thing. No complaints about Fire being OP on the PTR. No additional proposed changes or nerfs in patch notes. Nothing.
5.1 goes live, and oops, the change to Combustion ends up being an accidental buff. But instead of reverting the changes, after two days, they nerf combustion to be merely 50% ignite, *and* they nerf critical mass to 1.25. The critical mass nerf was never brought up, mentioned, discussed, and certainly wasn't deployed on the PTR. Again, the only discussion regarding fire from the developers, GC included, were tweets about PvP.