2 and 1/2 suggestions:
Weapon 1: "Heirloom"
Perk: Support, +Sharpshooter
Function: 8 gauge pump action shotgun with slugs and scope, massive, and barely capable of handling, with the traditional "hunting shotgun" look, maybe. Single target damage taken to the extreme. Slugs do not penetrate (without perks?), maybe has quick dropoff and doesn't do much for range as Sharpshooter, but is very high damage-wise either way. If target is armored, does a ton of damage to armor. Long, satisfying pumping, preferably with a loud, realistic, metallic slide. Low powered scope with a square, sort of empty reticle. {This is all just in my, vision, obviously, there are many ways you could do this, and well.}
Reasoning: Support has so few fun late game weapons. I normally just find myself sticking to the frost fang, maybe pick up an aa12 that I barely use. That said, I'm an ultra-casual (in general) who mostly just plays hard and suicidal, and this just sounds fun, which is my main priority. Maybe make this sharpshooter first, support second to make it so support is receiving for once and sharp is giving for once? Or just take it off sharp and don't give them what is effectively another AMR but better? Also, game needs more pumpies.
Weapon 2: American 180
Perk: SWAT
Function: lots of bullets, not a lot of damage, but oooh, does it have a lot of bullets. Mid game bullet hose that sort of serves as a tommy gun on crack. Ultra low damage, 180 base(?) mag size. 3 mags in reserve, base.
Reasoning: Going all in on volume of fire and fire rate might be fun, considering the smgs kind of only differ by tiny amounts. Pop some variety in there.
1/2 bit: if you implement the firebug throwable, might I suggest one in the style of a hacked up oscillating sprinkler that squirts gas, and sends sparks out every once in a while, igniting gassed enemies, who also spread fire by touch now, or maybe the gas is just flaming/napalm? It'd fit your purpose and your style.