devilgrove Update to this:
I disabled AppleIntelICLGraphics.kext and AppleIntelSlowAdaptiveClocking.kext, and the display is now exactly like Safe Mode (as far as I'm aware). The only problem with this is that the display rendering is just as slow and just as glitchy as Safe Mode as well. Not sure if this is usable for me in the long run, but for those who can use Safe Mode but want full access to their Mac, give this a go.
Also, I have a rough idea of how I would go about trying to keep Safe Mode-level strain while being able to speed up the rendering. AppleIntelICLGraphics.kext is broken down into four bundles: The GLDriver, MTLDriver, VADriver, and VAME bundles. My theory is that I could disable or modify a combination of these bundles and keep ICLGraphics.kext enabled so that the render is back to normal speed. If anyone has ideas it would be appreciated, thanks.
Edit: too many applications required the use of OpenGL / Metal to run properly, so I reloaded AppleIntelICLGraphics.kext. I'll try to think of another solution (if there is one).