To fix it, I had to fully disassemble it, remove the Logic Board and access a tiny SOIC8 chip (the chip containing the UEFI firmware) on the BACK of the LB using the POMONA 5250 clip and then dump the corrupted firmware (will explain why), then reprogram the EEPROM with a Raspberry Pi and 8 cables with a dumped original firmware I had downloaded. You cannot download every original dump for every Mac model, every dump came from forum users and I got lucky to even find one for my machine.
Then, I had to open the corrupted dump with a Hex Editor and find the Intel ME region and how long it is, copy it to the new downloaded dump (without a clean or original ME region your Mac will be unbearably slow) and also find the serial number and replace it with my own. Then I had to reprogram the chip with the new, modified ROM.
Also, the chip is so damn tiny the clip could not make proper contact and I had to physically remove plastic from the clip to further expose the contacts and hold it in place by a contraption of lego bricks and elastic bands. I had to try over an hour just to make stable contact.
All in all I spent countless hours researching and waited over a week for the damn clip ($25 btw + $4 for cables) to arrive.
8/10 experience cannot complain but wouldn't recommend.