Vehicles is usually about teamplay. Because count of vehicles is less than count of players.
So about teamplay:
*) Armor seats with able to fire primary weapons and rpgs is required thing. Yes its more dangerous than seats inside. But there's immediate evac and ability to oversee battlefield with your actor camera.
*) BF improved idea that any "inside" seat should increase power of the vehicle twice, but increase complexity of teamwork between crew. Minigun AND turret (like in tank) should be on APC too. It could solve the trouble "who first get the APC = the pro". Also - no night-vision/thermal inside gunner seats and no ability to switch some useful thing to that useful thing. Even russian old btr had a nightvision scope...
*) In BB that feature is useless in humvee, because almost no armor and much of holes where is totally no armor. Your humvee its like BF light jeep that was ULTRA fast (and ULTRA controlable as driver like your quadro) and used to transport and spot most of times. So seat with MG and Driver CAN NOT increase the firepower without teamwork at all. If you imagine HOW, it COULD work. For me - one possible gameplay on jeeps - is keep some hill in 200 meters from fight zone and shoot from there, but new spawns time to time drives me to fight zone then we all dies. Also you made bullets of humvees very slow in Browning. With range most of weapons 100+ meters fast flying bullet is not a problem at all. That problem borned in Battlefield because you cant just kill the humvee gunner in 1 sec, you have to risk and keep time to targeting for, thats why some miniguns made slow as a bullet speed. Also that browning miniguns in BF have third times more brighten tracers. The idea is shoot 1-2 shoots to show the team WHERE is the enemy on servers WITHOUT 3d-spot.