Good AI knows everything and all optimal paths and choices but then is limited in choosing the best path through obfuscation
What? _No_. Good NPC AI has the information its agent would have and does what its agent would do with it. The metric is, how fun (it's a game) is it to go up against the agent.
So have zombies switch paths when they're blocked, with varying amounts of foresight, varying amounts of tenacity, and have zombies that encounter success overcoming frustration scream, attracting any frustrated zombies nearby. When choosing a new path, some zombies go straight for the target, some will detour to destroy weak things, some try to get above you, some try to get below, most try to go right or left or above or below or behind any zombie they can see that already has a plan, some will detour to destroy anything warm or bright, none of them like cold stone, some will climb, some can't, some rare ones will plan ahead through multiple visible obstacles, they probe for weak spots and are frighteningly good at finding them. They all hunger for your blood.
You've got nice variety in how the zeds behave in melee, that's a really fun minigame with horror-movie-level plausibility, as in, you're here to be scared, not convinced the real world actually works that way, and even the little girls will
kill you if you let your guard down for even a moment. They're predictable enough to suck you in after you think you can predict them. Repeatedly. Yay.
So go all fugue on that theme with the horde-attack AI. Reward players identifying zombie personality types, the types distributed like loot, random but you're likelier to get layered planning and exploration and and screaming-at-foreseen-weakness from screamers and up.