This has a grain of truth to it, but as someone who plays double battles almost exclusively, I can tell you that it's not quite accurate. Garchomp may not have been seen much in this latest VGC, but that's because he didn't fit well into the game that the Ubers created.
Garchomp, in general, is a complete beast in doubles. It's much more powerful than the average fully-evolved Pokémon. Fast, powerful, STAB Earthquakes and great type coverage are nothing to sneeze at, and they're a relatively rare commodity. Its 102 base Speed helps just as much in doubles as in singles, and with a Yache Berry it can do some major damage before going down.
The game is more balanced for doubles, but only if you take out a lot of Pokémon. If you allow Kyogre, for example, the whole metagame is always huge rain-fest. That's not what I would call balanced.