This will increase arms damage while not under the effects of Colossus Smash but nerf it DURING Colossus Smash. This means less burst, which is what you're whining about. I also don't get where you get "56k damage in a global cooldown" from. Jobdone has already laid it out, but you're just trying to over-dramatize it.
Aurora, I agree that this is a nerf to Fury damage in PvE. I bet that this isn't the final PTR and they may have a slight buff to make up for it in the future. The reason they're buffin' arms so much is that we rely on CS a lot more than you do, so I guess from that standpoint it makes sense.
Knusern: is Colossus Smash's armor reduction equal to that of armor penetration? With arpen in wrath, 100% "armor penetration" reduced target armor by a variable amount depending on how much armor they had. Colossus Smash's tooltip just says it ignores X% of the target's armor, so vs. any target it remains a constant flat percentage of their armor.
edit: I like PVPing but am not really serious about it. I am kind of getting sick of people whining about warrior damage and blizz handing out nerfs as a response. This screws us PVE players bigtime. I have realized that, as arms, I can roflstomp certain other classes in BGs, but am countered by any player who is good at pvp unless they're a lock or shaman (). Seriously we get kited by a bunch of classes. I don't think "mages are OP and I should whine to the forums about them" because other classes counter mages too.