Even if you can control their AI with wood, you still want fairly durable blocks in case damage causes a disruption. I can't pin it down, but at some point the AI will decide it won't go around and decide to make its own shortcut. High HP boundaries discourage shortcutting by smashing. That's one of the big reasons I always double-up my doors. Normally doors are pretty low hp, but having two in succession significantly curbs attacking my own in-out path.
You want two things: You want to focus the enemy horde towards a fairly manageable combat area so you don't need to worry about 360 degree defense, but also provide them enough variety in access route so that you don't overwhelm static defenses like spike traps, barbed wire, electric fences, or blade traps. All of these take damage as they deal damage, and pushing too many zombies through can destroy them all, at which point you have NO defenses in that area.
For example, in my base:
I have a barn. One side is next to a POI, and one by the road. These are my 'rear' sides and I just have a perimeter wall and high-hp doors.
On the sides where I have room to work with, I built a trio of three 2-deep, 6-wide pit traps where I have VERY obvious holes in my perimeter wall. One for right-side zombies, one for left-side zombies, and a center one mostly as a fallback. These pits are filled to ground level with spikes so that zombies REALLY want the freebie route, thus become mired in a pit, but as the spikes dissolve from dealing damage and being randomly attacked, they become trapped, their friends route over fresh spikes, and I give them a greek fire bath. Once the trap is 'spent', they start piling into the central failover pit where the same thing happens.
After that, of course, is basically them running around in my barn while I quickly run out of ammo. I'm not in any particular threat, they tend to not cause much damage, but for a SP effort, I make a good accounting of myself with the resources I had to throw at them.
I'm seriously considering, once I have access to electric fences, to add some 'bug traps' along their normal pathing routes around my base to soften them up. Basically 8 electric fences zig-zagged across a 3-4 block wide tunnel where they normally run by. I'm also seriously considering an extended perimeter wall to include my exterior workspace and farms to have better control of the approach angles, and possibly add more bug traps.