This may not make them "better" than Riflemen on an individual basis but as a massed blob of 3-4 units they seem to be more effective than the same number of Riflemen.
Gren blob is the easiest to punish with heavier weapons though. Tanks, artillery, whatever you wanna hit it with, a gren blob will be hurt most by it since they're 4 men. Easiest to wipe those squads, especially if they're clumping themselves for you
They are annoyingly good against MGs with their rifle nade and lmg42. But same can be said for many lmg squads