Mr. Terrific and Doctor Sivana vs GLC

These two geniuses get three years prep having the resources of the JSA and the JLA (no outside help though). They face the Green Lantern Corps.

Second scenario, they face the Green Lanterns and the Guardians.

Battle takes place in Mogo's orbit.

I'd think that in 3 years and with those resources at their disposal, Sivana and Terrific could at least find a way to disconnect the GL's/Guardians from their power source. /shrugs