Ran the flash-all script in fastboot.
It's sucessfully flashed the bootloader, boot image and recovery.
It is now been 40min on the "sending 'system' (736772 KB)" stage.
It doesn't usually take that long, usually a few minutes.
I'm thinking of flashing twrp again and then flashing a stock rom but can't find a non-rooted version to flash through recovery.
Any help appreciated, thanks!