I don't know why everyone seems to think Rifle Grenade is some sort of mini-nuke, it's got the lowest AoE of all normal grenades. Except the Volksgrenadier Grenade, which is identical.
I think people are not frustrated by the statistics of the grens rifle nade, like you say nothing above and beyond that which is available to any other faction.
I believe its more to do with how it is delivered within the game mechanics. Its damage and AOE are what kill units by definition, but the cause of losses to a rifle nade are more abstract than simple statistical value of the nade.
Its one of the more subtle animations too look out for, added with the range and speed of the nade, makes them very hard to avoid just one, and impossible to avoid multiple.
With other factions you get a more obvious animation, but also a detonation timer which near triples the time given to react and move compared to the rifle nade