Good News!
I've found the origin story for FTWD and it's a movie from 1984 called 'Mutant' starring Wings Hauser! A movie so bad it helped bankrupt FVI and send its producer into hiding yet has loads more zombie action than FTWD despite not actually being a zombie movie! I concluded this must be the primary influence for FTWD by using the FTWD checklist:
Drab main characters who's deaths you're rooting for? CHECK!
Plot holes you could drive an MRAP through? CHECK!
Pointless non-stop character emoting? NO! Thankfully, it wasn't necessary.
Zombies, well, mutants that actually pose a threat to humans? CHECK!
Here's a screenshot. Enjoy.
https://postimg.cc/cKSBwSYb