I don't think scoped weapons have damage falloff. Will have to check source code though. For other weapons damage is halved at max distance (2500) units iirc.
Your smg is superior on medium range and still very competitive at short and long range. Not enough? Plus having extra hp by being medic, hp regen, less aim kick (current hp affects aim kick) and medpacks. I don't think adrenaline is needed.
And you can always ask a teammate to counter-snipe!