Well the only games I've played at recently have been semi-only, so generally HPA guns are much more prone to being abused in that situation since it takes a ton more work to get an AEG to the same level of trigger response. I think that a strict limit on the number of mags a player can carry would help to prevent some of this. I know hi cap bans are becoming more popular, but it doesn't really place a limit on the amount of ammo players can carry, it only changes the way that ammo is distributed between mags. I know Milsim West actually issues the ammo to players to limit how much people can carry. I'd be open to this idea as well, but I've never actually tried it myself.
Obviously you can't count on everyone to follow the rule but hopefully additional limits would help to some extent.