Your approach could appeal to that result as signature weapons need better balancing. Playing with the cost of accessories could also help with this.
Personally I would like to change the buff. Assault can equip 2 types of ammo, engineers explosives will reduce movement speed, support will suppress (old version) and recon can swap between regular scope and thermal (same scope)
However you slice it i agree that accessories could appeal players to use signature weapons.
I'm personally not a fan of giving each class a specific and niche bonus, as I believe this results in a convoluted system (similar to the current one that is implemented). Additionally, the bonuses you described are available to all weapon types, which would not incentivize players to choose the weapon type that is signature to their class. I firmly believe that there should be incentivization to get players to play the signature weapon type of their class, though that may be because I would prefer a closed weapon system in general.
