I'd assume that more than one grenade is thrown, as well as more than one burst is fired when using yr rifles or MGs.
As for the grenades effectiveness, my personal opinion is that now it is slightly, but just slightly overstimated, but anyway better than how it was in previous versions...
There has been a lot of "noise" in the past by many endusers about the too low effectiveness of hand grenades, so Matrix twicked them up, maybe a bit too up

Same goes with vehicle immobilization following a wall/building breaktrough: people claiming abt a so high chance(not far from 100%, indeed) to get immobilized not to be realistic; now I'm still waiting to run into an immobilization due to wall/buildings, with version 7.1....