Interesting comparison, thanks.
Since diesel fuel contains about 15% more energy for the same volume than gasoline, the Pilot and Colorado are using about the same amount of energy to haul themselves and the trailer, and the Touareg wasn't much better despite not meeting emissions regulations - diesel efficiency isn't always very impressive. Of course the big gas engine of the Q7 hurts efficiency.
The Q7 is Audi's version of the VW Touareg or Porsche Cayenne. The new Q7 is on a different platform from the 2010 Touareg, because both models were updated (in 2015 for the Audi and 2018 for the VW), but the engine is probably the biggest difference, although the Q7 is a bit larger.