Specific answers to unknown situations are guesses.
FOr a successful tiled installation, first, the structure has to be stiff enough to support tile (typically they use L/360 for that with ceramic tile, L/720 for natural stone). THen, you need proper subflooring, installed correctly to account for deflection between the joists. THen, there are numerous TCNA methods described in the handbook that show how to install the actual tile and have it be successful. IOW, there is no one way that works in all situations, with all materials, in all places. SOme methods are rated residential, some heavy industrial, and what may be good for one is not likely good for the other. The industry guidelines are a minimum, they have a certain margin of error about them (they are tested multiple times to verify that they work). Some never like to utilize the minimum, and especially where it may not add much to the cost or complexity, going overboard may be reasonable, or if there is uncertainty of the original assembly (the test procedures are with new, properly installed materials - you often may not be starting with that, so more can be justified, sometimes).
Advice is free. If you follow everything John says, you'll spend more time and money and MIGHT not achieve any improvement in the end result, and he has shown some methods that literally failed. I tend to believe the manufacturers know their products and have satisfied their many thousands of customers to have stayed in business and expanded. That John choses to ignore that fact and tries to reinvent the wheel on some things is fine for him. It just doesn't always correspond with reality or a budget. You don't have to spend huge amounts for an end result, but you do need to do what you do well enough. It's your decision on what is more than enough, and in that, I abide by the industry standards, not John's.