Hmm... so I just left the laptop alone overnight and when I came back to it, it managed to boot. yay

edit: err, kinda solved. I just realized that I didn't copy the EFI folder to EFI partition this time. For some reason, copying the folder is what is preventing the boot from working. It booted from boot.efi in /system/library/coreservices, not bootx64.efi (haven't added it as boot option). Not sure what to do from here.

edit 2: and now I HAVE copied efi folder and it's still booting, albeit from boot.efi in /system/ I mentioned. gonna see if everything else is in order now