Skarmory runs Shed Shell so it can escape Magnezone's Magnet Pull, and Magnezone isn't really threatening to any non-Steel type. Chandelure can actually threaten Pokemon that aren't Steel-types.
Also, try running a Shed Shell on, let's say, Chansey. How the fuck are you going to take hits now?
Which only implies that Chendelure is simply the same kind of threat as Magnezone, not that it's broken. The question is, how good is too good?
By running Blissey. I didn't see any Chansey in OU from gen 2 to 4, because it was strictly outclassed by its evolution. In a metagame where walls need to either beat Chandy 1-on-1 or run Shed Shell, Chansey won't be able to do either, and will fall back to UU.
I've been playing DW and right now will tell you Chandelure is the BEST poke in the whole meta. No, not soul dew latios or latias. Chandy can revenge those too; from experience unboosted shadow ball can 2HKO both of them. Choiced pokes are basically nonviable, and many slower users weak to Chandy's attacks are essentially screwed. Wobb was Uber last gen just because of Shadow Tag; Chandy has a viable movepool, good stats, and Shadow Tag.
Also, people arguing to put shed shell on walls is kind of dumb; as lucarioarkz said are you really going to put shed shell on chansey and other walls? Especially walls like SpD tran without recovery; they NEED the leftovers bonus every turn. Don't compare this to normal OU, because if Shadow Tag Chandelure was released in Normal OU, I guarantee the very next suspect test would ban him.
All you're telling me is that Chandy is the reason some pokemon can't be used in OU. Does that mean he's broken?
Also, for the longest time the Dream World section of Ferrothorn's article suggested that, even though Ferro got nothing form the Dream World, it should run Shed Shell when DW Chandy got released.
I'm not denying it's a threat. I'm not doubting that it's the best poke in DW. But if you're not prepared to stop a threat, it can sweep you. That goes for anything.
Then again, if it is like Excadrill in that it does put an unnecessary strain on the metagame, I'm all for banning it.