That is exactly what I was doing, but still the camera was struggling with the extreme difference between people in the stage lights and the dark background, varying the ISO way more than it needed. going full manual in my situation has greatly improved the quality of my photos. on average, I shoot at ISO 800, 1/125, 2.8, although at our recent Christmas production, we hired in additional lights, and I found I could drop my ISO to 400, increase shutter speed to 1/160, and even narrow the aperture to 4.
But this is a very specific situation. Under stage lights, I have found there is not much need to vary the exposure settings, but the camera kept changing its mind on what settings were required, and I needed to be very specific where I set the spot meter on. with full manual, I can set everything to what is required, and just concentrate on getting the focus right. No need to try and make a decision every shot about the exposure... once you have the settings right, just shoot away
Mostly I do use auto ISO and aperture mode.