Yes the things you outline are an issue, and we have a number of plans to deal with them.
Vehicles are still stupidly OP in a number of ways, and we’re planning on reigning that in.
New challenging areas like more dangerous labs, large bandit camps or through-the-portal areas are certainly an option for very late game content.
Player melee combat ability vs hordes of zombies is just silly broken. Mobbing behaviors, stamina drain, and advanced grappling attacks should tip the scales in the other direction and at least present some interesting combat challenges.
Ranged vs zombies need a meta nerf via hordes, a.k.a. wandering zombies, but they work. I.e. gunshots in a city should be actually dangerous.
Zombie composition can also be improved, right now zombie evolution is partially done and we aren’t comitted to it, so the mix of zombies is a compromise that falls apart at higher levels. The plan is to have all the zombies start out vanilla at game start, but appear in much greater numbers, then over time they evolve to more dangerous versions, including some new versions that should shake things up a bit.
Labs need a total overhaul for difficulty, none of this weedy SMG turret fire you can just tank with the right gear. I dont want to just up the damage output though, we need to plan and execute on some real security measures and/or tough monsters for labs, along with overhauling layout.
Enemy NPCs are definitely something that needs to be in the mix, though I don’t know how soon that will be workable. We have plans for how it will work, but the infrastructure to make it happen is more extensive than anything else here.
Hope that lets you know the direction we’re headed.