Regarding zombies
I think it would be a great idea to add an extra item slot only for "special items". These items could be the vaccine for the t virus, or melee weapons that spawn around the map and can be used to kill zombies. Maybe have them be one-use and respawn randomly around the map.
This way we would have a more consistent way to defend from zombies that doesn't depend on wasting pallets (which are a very valuable resource), or flashlights, which i found very inconsistent, going from A) Not having a flashlight and not being able to do anything about zombies, to B) Having a flashlight and completely disabling zombies for free.
Having to look for weapons around the map makes it more fair and adds new objectives for the survivors.
This still doesn't fix the problem of running from the killer in a hallway and having a zombie blocking your way and just dying unfairly. Maybe you could use the weapons while runnning? Idk just some ideas.