Specsmence is beaten by Bliss, Empoleon, and Regice. Mixmence is beaten by Tentacruel (none have EQ BTW) or Cressilia, physical 'mence is beaten by bulky waters and Porygon2.
The biggest reason people complain about Garchomp is because it has no surefire counters. By your own admission, doesn't this indicate that Salamence has no counters?
And on the subject, you could say that nothing switches into Garchomp. Given that, what exactly can Garchomp switch in on? Anything physical that comes from a 115 Base Power from 130 Base Attack is gonna take off more than 50% of Garchomp's health, and from the special side the base power is 102. This is merely a STAB 70 Base Power Attack. If the 130 Base Attack seems too low, then certainly a stronger attack from a lower base is gonna be about the same. I'm sure the scaling is easily done in your head. There are a lot of things that are faster than Garchomp with 130 Base (Special) Attack. Weavile makes sure that Garchomp can't switch in, Gengar, Alakazam, Azelf and Starmie are all examples just from OU that are faster than Garchomp and have a good shot at OHKO'ing. I'm sure that you'll say that Sand Veil can help out here, but there's a good chance that two of these are going to be on your team. Let's say you have a TrickScarf Alakazam. Then one of a few things will happen when I use Trick (guaranteed to go first). Either you will have a SDChomp, of any kind, and the Scarf will cripple Garchomp. If not an SD, then either Scarfed or Banded. If Banded, then that implies a Jolly Garchomp, which means that any of my walls are going to both know that you cannot stat up and that you won't be doing tha much damage.
If you have a ScarfChomp, then not much happens outside of me knowing your set. I can try to Knock Off, but I think that if I assume two pokemon on my team you'll cry out "overcentralisation".
If my Trickzam has Specs, then the only difference in this entire scenario is that ScarfChomp's that switch in on the Trick are going to lose to my Timid/Jolly Salamence, at the cost of an Alakazam.
