So I tried upgrading my server today for security and feature updates and such, only to find that almost all the stuff related to mysql had been completely borked.
Now, after a while of trying to fix this, we just decided it was easier to uninstall mysql-server and restore from the backed up db (which we had from the same day, no data should be lost).
HOWEVER there seems to be something wrong with ubuntus packaging of mysql server, because even when having purged every single package related to mysql, and every config file or storage it used, it still failed to install and setup properly.
In the end I decided to try mariadb, and lo and behold it worked instantly.
Isn't software amazing?