You might want to view this test report from the Gypsum Association about the shear strength of gypsum board
http://www.grabberman.eu/Media/TechnicalData/450.pdf . You will get a very significant difference in shear strength based on your screw spacing. But, consider that the specs for all bonded membranes to whatever substrate you choose is that it must be over 50psi (and Kerdi generally tests out upwards of 75psi). So, the thing you should take away from this is that the bond strength of the fleece on a bonded membrane, I don't care whose you choose, will be less than the strength of the substrate, drywall included, by a factor of at least 2, and under ideal conditions, over 8 if you choose the smaller spacing used in the testing.
A double margin of safety is plenty. An eight-fold one is way overkill, but easy to attain, if that floats your boat. The fact that two significant companies in the industry allow their membranes to be installed over drywall, and one that has been doing it for over 25-years with success in a shower (Schluter's Kerdi and Laticrete's Hydroban membrane - Kerdi is by far the older one) would seem to make John's argument kind of misguided. If you install the membrane properly, it passes all of the A118.10 tests and has been certified by independent testing to provide a totally waterproof shower. What more do you want?
Thin has it's advantages - all corners done with a bonded membrane will end up with 3-layers on part of it. John's preferred one is 3.5x thicker than Kerdi. That Noble membrane will end up being 90-mils + two layers of sealant thick or about 1/8" bump in the corner. The Kerdi corner will end up about 24-mils plus two layers of thinset, about 1/4 of the overall thickness. Given the TCNA guideline of no more than 1/8" in one foot out of plane for a smaller tile, and 1/16" for a big one, guess what...the simple, required act of making a waterproof corner puts the surface out of tolerance with the Noble membrane. Should you need greater perm rating for a steam shower, Noble will give it to you, but so will the thicker version of Kerdi (KerdiDS), and it will still be a lot thinner.
Just goes to show how far John will go to trash a company. If you really want to, both Schluter and Laticrete have tested their membranes for use over lots of other surfaces, including a cbu, so you can use of the others (including cbu) if that makes you feel better.