Yeah, would be great if these were options you could fiddle with.
In the past I used ZomTorio but it isn't maintained for years now. I can change values and even behaviour via a config file but it's a pain in the a$$ and increasingly difficult with everything else changing (and most likely breaking with 2.0).
Anyway, I do think zombies have too low health now, so this is what I would mainly adjust in settings. It would also be great if we had different types of zombies that could be altered individually. Haven't played much yet but I think I have seen runners? Anyway, would be great to have the occasional armoured zombie with high resistances for example.