The reasoning for disabling buff guns on the ground is far from being outdated. We cannot have instant field ack by upping a buff. Player controlled guns does not mean the guns cannot be disabled, but if you allow planes on the field to act as serogate ack platforms, it makes fighter cap imposible without first destroying the hagners.
Please explain exactly what reasoning you would use to debate in favor of allowing buff guns to be fired on the ground? Yea sure in RL you could do it...but in RL there isnt a chance in hell a bomber crew would attempt (of be able) to take off from a field with enemy fighters buzzing overhead.