Excadrill was powerful in the sand, but it had a butt load of weaknesses, too. In fact, once Sand was down, it was really easy to take out. Not only that, but a lot of its weaknesses are obscenely common. And yet, it's still banned.
Shadow Tag Chandelure is deadly because nobody will use it unless there is a pokemon it can defeat out. Terrakion stuck on CC, Venasaur, maybe even Dragonite if it's armed with HP Ice. The point is, Chandelure strengths outweigh its weaknesses. Yes, it can be beaten, but like Excadrill and Thunderus, it's going to be too hard to do so.
I think it will be always top priority to beat before chandelure weak pokemon come to the field also ditto..
I guess a chandelure + ditto combo can work you go to something that is boosting with chandelure then if chandelure is killed ditto comes with boosted stats to beat a whole team :3