Hey thanks for your curiosity and willingness to dig into this with me!
So, originally I was trying to livestream with OBS. With my audio from Mainstage and video from the built-in cam. So I figured it was OBS and Mainstage/Logic Pro causing the problem. But even with OBS off, and even after restarting my macbook (yes, with nothing on startup,) if I turn on Mainstage or Logic Pro and the built in cam, even just in Photo Booth, the CPU maxes out and the audio suffers.
No idea if it always would've done this, since I've never needed to have the cam on while using Mainstage or Logic Pro.