If you do watch the videos carefully, you will see that Russell/9thgenaccord does indeed characterize the soap in both the foam cannon and the bucket wash. He characterizes the foam structure (bubble sizes, mix of sizes, and for foam cannons, layers) and lubricity for both the foam out of the foam cannon, and from the wash bucket. Lubricity/slickness seems to be a particular point of emphasis for him.In addituon, he has now started to rate how "durable" the soap is on the wash media. Durability is defined (by him) as how slippery the the media at the end of a panel being soaped up is as compared to the beginning of the panel being soaped up. That too, seems to vary. between soaps.
As for the validity of a foam cannon, to each their own. Gary Dean has his opinions. Others have different opinions. Considering the amount of time that setting up a foam cannon/pressure washer takes up to set up, vs. just a pressure washer alone, I like to take the extra 5 minutes, and 2 ounces of soap and foam wash. It may not be getting much of a benefit, but it may help dislodge some grit particles or get rid to some tree sap. Argument can be made that just a pressure washer rinse may do the same. Maybe. Maybe not. Just seems to me that a good to great foaming soap (high lubricity, high cleaning power) would be of at least some benefit. My soap of choice, CG Maxi Suds II, was chosen based on Russell's video of the soap. It wasn't the best soap, but it was among the soaps that cleaned the best as a foam wash. I hadn't even heard of the Maxi Suds II before watching Russell's video review of it. Without the review, I probably would have chosen some other soap, and it would have been hit or miss as to whether that soap would have done as good a job (considering the number of soaps out there, probably miss).
As for Gary Dean, or Russell, or Junkman 2000, or any of the Youtube detailing hosts, I do watch their videos, but I don't necessarily agree with their points of view. I respect their efforts, but they don't always come across as logical to me. Gary Dean has his views on foam cannons, and I don't agree with them. Junkman 2000 is a two bucket wash method guy; I use a one bucket method (like Russell does). Russell doesn't think that increased foam cannon lubrication will cause the foam to slide of quicker. I disagree because it seems only logical that a slicker/slipperier surface would allow gravity to pull the foam down faster. Junkman even contradicts himself sometimes. What I am saying is that there are many ways to detail a car. Everybody has their own way, and if it is working for them, great. I am pretty new at this, but did a lot of reading, an watching of videos before I got started from multiple sources. I took what I thought was the most logical parts of many processes and jumbled them together when I started doing my own detailing. Doesn't mean anybody was wrong, just meant that I used what works for me. I get a lot from the detailing videos, I don't let them think for me. They all provide some information that is useful, but they also mix in some opinions that I don't agree with. I couldn't for example, run out and get upwards of 50 car soaps to try in order to find the one that was best for me. Russell has done that in a video series, so I take that information to help me decide where to start. Where else are you going to get valid comparisons made? Watching vendor videos doesn't work; CG must have a dozen soaps out, and according to their videos, every single one of them is the best; all of them make thick foam, all of them clean perfectly. Guess what: NOPE.
What Gary Dean says about foam cannons may be completely correct in Florida. I don't live in Florida, I live in Calgary, Alberta, Canada. In the summer, we get a lot of blown dirt particles on everything. Our humidity is low, the summers get hot, it is windy most of the time, and dust blows everywhere, all the time. So, in our part of the world, I think a foam cannon pre-wash helps.