Duke William of Normandy won the battle because was well prepared and had a good army. They prepared carefully for the battle. The Normans had knights on horseback who were skilful fighters.
A utility knife, metal ruler, and a hammer can be faster than trying to carefully saw an opening. Score the drywall a couple times till you are most of the way through, then just knock a hole with the hammer and break the drywall back at the score lines.
Set the circle cutter to cut about 1/8 in. larger than the fixture, stick the center point in the middle and rotate the cutter while forcing the wheel into the drywall surface. The key is to cut through the paper. It may take a couple of rotations. Then repeat on the other side of the drywall and knock out the plug.