I always assumed Guard Motor was more popular than Guard Rifle. It's kind of hard to know how popular the PPSH was before the patch without statistical data from Relic (I for one, would love infographics. Some of the best things from community managers of other games are infographics...people love pictures).
However, a good indication of how popular certain commanders were, is by jumping onto team games. I play a lot of team games, and seeing PPSH cons were a rarity pre-aftermath. Lots of people rather rush vehicles. This is all subjective of course.
Exactly, there's no reason not to buy PPSh, it's a no brainer.
Well, it's no brainer for Grens to always go LMG whenever possible. Exception being that the LMG does drop at a rare rate after death. In the end, the PPSH is doctrinal, just like the G43 (neither are droppable). Though it might be awesome if any weapon beyond the standard rifle had a small chance or dropping.