@Acumental What level is your son at? I seem to remember you making a thread recently about this issue. And your son has only started this season, so he’s probably still fighting the really bad players.
Also, your son is probably exaggerating a little, as there are definitely other guns on par with the R-99, such as the Volt. The Wingman can be another, if you can hit your shots.
Advice: Your son should probably start to switch off the double R-99, especially on the Olympus map, as it isn’t going to work as well once he gets to the level where people can aim and use snipers.