Simple rule: Anything that is blocking zombies from reaching the player without being damaged or wasting resources is an (AI) bug.That is untrue in JaWoodle park yes but he has built many variations of the kill corridors actually in game and I never use creative menu but have built variations of the kill corridor in game, as I don't see using game physic such as the steep slope as cheese anymore than putting a block or spikes down in a doorway.
The arrow slit force field is an exploit but takes a lot of effort too do it right, and isn't really that worth it.
Trader compound is the obvious exception.