I think as guitarists we're WAY to quick to point towards the transformers as being something that instantly has a noticeable effect on tone when 9/10 its something far more straightforward.
I'm not saying transformers don't make any difference at all, but you have to rule out other factors like valves being graded differently before assuming its that. The difference transformers would make, particularly at low MV settings where they are operating in a comfortable and linear way isn't going to be that noticeable as what the video shows.