I'd be fine with Arms having a better ST niche while Fury did a bit better on AoE. That's good spec design I think, so long as the difference is manageable. A 100k DPS difference is not what I'd call manageable, however. I'd be OK with Arms doing 5-10% more single-target when played optimally, but not the giant gulf that exists right now between the two specs.
I mean, I also don't believe Arms is going to escape a heavy nerfbat, but that doesn't help warriors much if Fury's ST goes untouched. We shouldn't be top of the pack, but being so behind the top specs is not really acceptable class balance, especially in Legion where switching class/spec is made harder, even if not that hard.
The 30% damage penalty, while not incredibly major in the grand scheme of things, just adds insult to the injury of our low-ish damage, on top of killing any possibility of Fury ever being viable in PvP. Yes, Fury is fun to play so I'll play it, but what's the point of making us take extra damage if we can't even dish out significant pain in return?