Yeah, I'm another that hasn't played DW, but I find it difficult to believe that Chandy won't be broken with Shadow Tag.
Other trapping pokemon have nothing on Chandelure. Magnezone can only trap steels, and of the steels it can trap, it can't necessarily even kill them all depending on the moveset (i.e., Scizor can carry both Superpower and Brick Break, which can screw over Maggy if it doesn't have HP fire). Really, Magnezone is almost exclusively used to beat Skarmory and Ferrothorn and I can't think of much else that is noteworthy that it can beat (Scarf with HP fire might beat Lucario, but even then there's Vacuum Wave to be concerned about).
On to Dugtrio, and while it can trap a lot more than Magnezone can, it's pathetic base 80 attack means that it can really only trap and kill things that are specifically susceptible to ground type moves. At the moment, I'm thinking Tentacruel, Ninetales, Tyranitar, Heatran, maybe Darmanitan (though only if it's not scarfed, which is common) and actually, it's not a bad list, but they're not guaranteed kills either. Ttar lives CB earthquake (252atk/ 252spe Jolly), doing between 326-386 damage, and Tales and Heatran could be scarfed - and with Dug's paper defenses, it really can't afford to take a hit. Like, at all.
the only other trapper available to us is wobbuffet, which has the same ability as Chandy which allows it to trap everything, not just steels or with the exclusion of flying pokes/ levitators. Like Chandy, Wobbuffet too can beat pretty much anything; but it's a one-time usage. Wobbuffet can only sponge one hit to counter/ mirror coat back, and by then it's usually too weak to do much else. Admittedly it can be paired with Wish to make this better, and Wobbuffet can also encore/ tickle stuff. However, the main thing holding Wobbs back is that it's movepool + stats allow it to do only so much. Wobbs can't set up and sweep. It can't directly threaten (i.e., you could elect to simply use a non-damaging move, and just get encore'd, though you do give your opponent switching advantage).
None of the above pokemon can do what Chandelure can do. Say Chandy is running scarf: Unlike Magnezone, Chandy traps everything in the game, not just a few pokes; unlike Dug, Chandy can hit brutally hard; Unlike wobbs, it can kill stuff, without killing itself in the process. Then, take Sub CM: Actually, none of the other trappers in the game can set up at all, apart from Sub-charge beam Magnezone, and you can't really set up on much with that (i.e., skarm isn't going to be taking Charge Beams in order for you to boost, obviously).
Basically, the point of all that was to show that ST Chandelure is like no other trapper, and you just can't compare it to them. It's ability to revenge stuff with scarf is far more fearsome than Dugtrio, it's ability to set-up infinitely more terrifying than Magnezone, and, while I can't speak from experience, this thing could assuredly net more kills per battle than Wobbs.
But I'm not done. You see, there's this whole issue of 'countering' Chandelure. Now, take an obvious example of one pokemon countering another, like Conkeldurr counters Blissey. The only things bliss can do to conk are S-toss (which can be recovered with Drain Punch) and toxic/ t-wave, which activate Guts. In return, conk can set-up and sweep. Or just go for the OHKO with Drain Punch. It's a hard counter, because you can switch in with little fear, and instantly threaten the OHKO.
With Chandelure, a part of the equation is missing: You can't switch. See, with the Bliss example, even if conk comes in, Bliss will just switch (and not pointlessly die). With Chandelure, anything that chandelure beats, if it's in battle, dies. And don't think this is just reserved for pokemon that are weak to fire or ghost; with 145 base Sp. Atk, plenty of pokemon who are neutral to both are going to die to it. Still, if you look at stuff that is specially susceptible to it, out of the top 20 pokes, ScarfLure wins against Scizor, Ferrothorn, Jirachi, Latios, Skarmory, Reuniclus, Deoxys-S, Celebi and Forretress. That's 9 pokes, nearly half of the most used pokemon in OU.
BTW, I'm assuming the set looks something like:
Chandelure @ Choice Scarf
Shadow Tag
Modest - 4HP/ 252 Sp. Atk/ 252 Spe.
-Fire Blast
-Shadow Ball
-Hidden Power [Fighting]
-Energy Ball
Anyway, that doesn't count stuff like Gliscor, which can nearly be OHKO'd by Fire Blast (or actually can depending on HP investment - 0 Sp. Def/ neutral nature does 297-349 damage, with Gliscor's max HP being 354). Furthermore, 2HKOs will become OHKOs after a bit of residual damage. Rotom-W with no Sp. Def investment takes 208-246 damage, and Rotom-W's HP can strike anywhere between 241-304 depending on if your defensive or choiced. Either can be OHKO'd after a bit of residual damage.
Argh, I have too much to say. I need to stop.
However, to briefly run over my main points:
1. Chandelure can't be compared to other trapping 'mons
2. Chandelure can completely screw over 9 pokemon of the top 20 - nearly HALF of the top of OU.
3. The pokemon that Chandelure can't initially screw over at full health (like rotom-w and Ttar), it's fully capable of dealing with after residual damage.
4. The result of all this is that Chandelure is ridiculously deadly, completely changes the face of the metagame, and makes teambuilding completely centred around Chandelure (as having even one poke on your team weak to chandy becomes set-up bait for Sub CM lure, and is an instant liability).
BTW, this is a bit tl;dr. Still, I've come to the end of this post, and I'll be damned if I don't post it now, whether it makes sense or not :p