He actually might be wrong about the efficiency of the single-duct models, too. I read a counterargument that they actually work more efficiently than the dual-duct kind due to the fact that they're dumping heat into cooler indoor air to vent rather than trying to further heat up already-hot outdoor air. True, it causes some outdoor air to come inside in the process, but you're going to want some degree of air exchange anyway.
The newer systems for rating the efficacy of these units may ultimately account for all this. They basically make a mockup of a standard room and hot outdoor space, run the unit in it for a period of time, and then measure how much electricity was used to cool the interior by X degrees. Ultimately that's all that really matters - how much electricity gets turned into how much of a drop in indoor temperature.