I'm CMAS certified and that's the way we learned it.
Later when I was working at a PADI centre we had to teach the students to take the gear off one arm at the time and pull it from the side and place it on the leg, etc... But as an extra I sometimes showed them the other way and many of them found it easier because they are more stable.
I've also done it on the surface (but in the water) when taking out a twinset because the harness was a bit tight and that was the easiest way and I often do it when I'm kitting up (single tank only but I use either a 12l or 15l steel) because it's easier, faster and I don't need to ask anyone for help... In this case I have the tank facing me, I put my arms through the straps to the point where my elbows go through the straps as well and I grab the tank with my hands. But the weight is supported by the elbows and, therefore, the arms, not the hands as the tank could slip. This way is safer and you don't need as much strength.