we are talking about the sdchomp and were NOT incorporating all moves and items.
Good to nail that down.
So now, it seems to me that the other OU Dragon that runs a setup and sweep set has to be handled in similar asymmetric means to Garchomp.
I can't think of any one Pokemon you can switch into DD Salamence and blithely think it's a 100% counter despite the fact that you know the moveset.
Most bulky Pokemon will be 2HKOed buy some combination of attacks and fast frail Pokemon (which BTW *must* be scarfed to outrun +1 Mence) cannot switch in except on a predicted immunity.
This is not much different from SDChomp except that he has viable non-scarfed revenge killers!
Now, I'm not tying Garchomp's fate to Salamence's as a matter of argument, just saying that this search for a 100% counter is not as vigorously pursued for DD Mence.
So it seems inconsistent that this is insisted on for Garchomp despite the fact that it is vulnerable to similar strategies as those used to contain DD Mence and has a lower speed to boot.
Likewise, in UU, SubCM Mismagius can be very difficult to counter except by asymmetric means (trick, haze, encore, etc) since if it gets multiple boosts not much can absorb the attacks.
Stallrein is usually beaten asymmetrically as well by Tricking/Taunting or Phazing it since very few things can power through the Substitute/Protect cycle especially since it can Roar you if you try to set up.
So I consider the argument against SDChomp based on lack of a 100% counter - defined specifically as a Pokemon that can switch in, take a hit and kill it - to be a red herring in its case.
This was never a ticket to the banlist.