Mag has coverage and spies. Coverage allows them to D up while other servers are slow and the spies mean mag responds to were any organized group is going before it gets there, they also eat up queue spots if you can get a map queue. On top of all that SoS at least has a lot of quitters who simply won't log in to fight mag.
Some fixes would be allow teams to place siege in their spawn. Get rid of EWP. Add some stat upscaling to outnumbered.