Efficiency high PvP and general lack of PvE use is my guess. In PvP, you can get a lot of easy kills with a Machine Gun, even if you would just get 75% of a mag, if you don't miss too much it's a few really easy kills. The obvious balance would be to reduce ammo, right? but at the same time, wouldn't it be kind of stupid to give you a machinegun where you never get more than 50% of a single magazine If they give it too low of ammo, they get dominated by the other Power Weapons. They probably tried it out, testing out if they can get the right balance without making it feel like you got unusually low ammo, but ultimately chose that it wasn't working. AAand is probably why we're getting Sweet Business. Then there's PvE. Save for some niche guns, they're underpowered in PvE, but not because they do too little damage, but because their damage only shines if you SUSTAIN it (Ie stand in front of your targer and shoot out everything), which except against raid bosses and their specific damage phases, other bosses this doesn't work out so well as they just hammer you down. I wouldn't mind seeing HEAVY turrets take their place. I'd say think Halo mounted turrets. In Halo you could break off turrets and tote them around until the ran out of ammo, and the balance for this was that they impaired BOTH your aim and movement speed.