Yes, yes, and yes.
Rifles are long, have three points of contact with the shooter, and enough weight to negate a lot of the recoil. They make a very stable and accurate firing position, which is why the fundamental design of rifles hasn't changed much since the old muzzleloader days.
The PPSh has a MUCH higher rate of fire than the MP-40, and fires a larger bullet. The MP-40 is very controllable for an SMG, even by modern standards.
Old woman shoots MP40 Machine gun - YouTube
LMGs, on the other hand, shoots full-sized rifle rounds at blistering rates of fire, meaning they generate an incredible amount of recoil. This is why most machine guns are mounted on big, heavy tripods, as they help control a lot of the recoil. Bipod-deployed LMGs have a much harsher recoil, as they're relying on the shooter to brace them up, and humans simply can't compensate for that kind of vibration through sheer muscle power alone.