What am I missing with Medic and Support's DLC guns?

If I die to those classes played by lvl 150s, they're almost always using one of the DLC guns: for Medic it's always the Avtomat/Farquhar-Hill/Howell Automatic, and for Support it's always the LMG 08-18/M1917/Parabellum. And it feels I'm always outgunned by those guys as long as I'm stuck with the base-game guns.

For the LMGs, I could see they're arguably just better versions of base-game guns: the LMG 08-18 and Parabellum is just a better MG15 thanks to their higher RPM, and the M1917 is just a better Benet-Mercie thanks to its bigger magazine and lower recoil+spread. But maybe there's something else I'm missing here.

For the self-loading rifles...I'm really stumped. They seem to perform similarly to the base-game guns. I'm not sure why the DLC guns are preferred over the others so drastically they're used game after game by those players.