First off, I'm glad to see people who share the philosophy that 'overpowered guns' shouldn't determine the outcome of a fight. If I had more people that share this idea, it wouldn't be a problem to nerf handicap guns like the BAR and Souizen.
Second off, this isn't a bad idea. We had something like this on PC Era at one point in time, that only allowed single handgun-tier weapons(single AP7, single DEagle, Single P2K, Single Handgun, etc.)
I personally never sparred in it, because guns were balanced back then and it really was just for fun. It was also short-lived because nobody really used it.
I think it would have more use on iEra. Guns like the BAR and Souizen ruin the game, and I can't even do anything about it because there are too many people who paid for that handicap; and would rather hide behind it than acquire skill.
I often think about saying "the hell with it" and just start nerfing these handicap guns to be just slightly better than the rest, instead of extremely overpowered; and then reimburse people with the difference in statistical value in gralats. (I'd nerf the BAR to be worth about 120k and BAR users would get back about 80k)
Simply because it's for the good of the game to amplify competition and make guns more variable.