My suggestion: create a brand new class for MMGs and AMRs, removing them from the Support and Recon classes.
Nerf infantry damage for AMRs and recoil for MMGs, while looking to improve their performance against tanks and planes respectively.
In turn, allow this class special access to better secondary weapons, along the lines of the tanker/ pilot weapons for BF1. Machine pistols, double barrel shotguns, pistol carbines, that sort of thing. This way Heavy Weapons players have an option for mobile and aggressive play.
Gadget option suggestions:
Deployable shield (similar to BF1)
Deployable tripod (for extremely good recoil control and a bit more elevation than bipod)
Grenades: Frag, AT, Sticky