First it was a 403 error directly after updating, tried chmodding 777 -R, no change, deleted .htaccess, turned into a 500 error. Already updated the database so there's no rolling back now. EXTREMELY irritating that the 'official' 3.2.7 > 3.3 updater doesn't work worth a crap.
I actually did get it to work by disabling every extension via the CLI. The extension that is causing the conflict seems to be the official phpBB site maker plugin, so I'll dig into that and make a topic in regards to that issue if the time comes. Thank you for your help.
In any case I was able to get it to function well enough, so you can mark this as solved. Sorry for seeking assistance prematurely, and you're correct, I should have started by disabling the extensions before upgrading, but now I learned about CLI and can do much more troubleshooting myself in the future