also the magnums still exist

So, I tried this out on the first level of Dead Center, and noticed that there were a few holes in your scripting, unfortunately. After using up a chainsaw, I was given a pistol, and was able to acquire a ranged weapon that way. Then, on the bottom floor, the manually-placed SMG and shotgun were still there, and from that point, the game was no longer melee-only.
I dunno if it's possible to make the player receive a fire axe instead of a pistol upon using up a chainsaw, but might I suggest replacing ranged weapons with assorted melees instead of not making ranged weapons spawn at all? Like how Last Man on Earth dynamically replaces tier 1 weapon spawns with tier 2 equivalents. Dunno how you'd work out what gets replaced with what, but grenade launchers and M60s could definitely be replaced with chainsaws, since they fulfill a similar role as an unreloadable power weapon.