I suppose I misspoke, but my point was that a single Romero zombie shouldn't be that tough to kill at all. It is, after all, a slow, stupid creature with no sense of self-preservation or any protection aside from its bones and ability to not give a shit about having big holes blown through it. The classic Romero zombie isn't something that should take someone a while of wearing down to kill if you have some idea what you're doing. It's when there's a bunch of them, and you don't have time to bring them down one at a time, that the consequences they can take come in to keep them going, and they become a real threat.
The way I see it, a single zombie faced by a group of PCs, or even a lone PC, shouldn't last more than two rounds--one to pull a maneuver or inflict a strong consequence (any PC with a weapon and half-decent attack skill ought to be able to manage it, given the zombie's 0-base defense roll), two to blow its brains out and finish it off. Unless it manages to get the drop on someone, and barring freak good/bad rolls, it shouldn't be able to do much damage. But if the PCs are significantly outnumbered, sure they might still be able to finish off individual zombies, but each time they concentrate on one, five or six more get to move in and attack. The tactics shift to crowd control and spray attacks to make breathing room--inflicting consequences, possibly Severe ones that all but cripple the zombies, but no true Take Outs.