I think, to avoid predicatable behaviour we actually need more than one AI Pathing logic. Like, so zombie follow the available path, going through tunnel etc, like they do now. But 20% of them just see you and come straight line to you, if any obstacle they hit it mindlessly and break it, and then start coming again. If you are on top then they hit near by pillars or dig ground. 5%-10% of zombie use both in a mix, that if they are 20 blocks away they go through available path, but when on 5 or less block away they rush straight line. This mix will make things more interesting and reduce load of AI path calculation on CPU as all are not finding complex path.