oh. my. god....
my MacBook is working again. i decided to try it again, being drunk with nothing to do. so i put an ssd in it that it previously didn't even want to format, and i just booted to recovery and tried to install macOS. to my surprise, it installed flawlessly, and it seems to be fully fixed. everything is responsive, it's running just as nice as it did when i first got it.
i am so so so happy right now. i have my favorite computer back.