I like the testing process, and feel it is good information, though, as he states himself, a narrow sample of 1. It is an interesting anecdotal bit of information. Despite being a narrow sample of 1 pistol, I still think it can provide some insight into any inherent flaw or weakness with a particular pistol and its ability to handle some basic elemental intrusion.
MAC is very clear about all this as well - these videos should not be make or break about if you like or dislike a pistol - just another piece of data to be weighed as you see fit based on what you intend to do with your pistol.
I was pretty surprised by the Sig as well; I expected it to fare better. Though, I've been issued a Sig P229 for about 10 years now; we replaced our aging fleet of circa 2005 pistols in 2012 due to frame cracking, and the 2012 Sigs are far inferior in fit, finish, and reliability from the older guns. I'm on my 3rd 'new' pistol due to continuing untraceable failures to extract and eject. I'm a Sig armorer, and can't find the problem - the only thing I can think is that there is some improper tolerance in the extractor spring and plunger channel causing erratic tension on the extractor.