In reality, they would simply break the bottom blocks, making the structure completely collapse (remember those early screenshots of what happened to the barn?

remember how we thought zombies would start whaling at everything, breaking it down instead of following stupid paths that makes gps tracking look bad?)
I think everything where you use the A.I. against them is absuing it.
I think everything that you couldn't do in reallife (more or less! I couldn't dig a complete shelter in 7 days but I hope you know what I mean) is an exploit.
If I hide on top of a huge poi, zombies should just start whacking at the foundation until it collapses!
If I use funneling, they should just whack every block (while some try to get to me)
If I use loops, they should not rerout, but just start whacking in frustration...