I will keep things brief, mostly by pointing to an instance of problematic hitboxes from another game series and the way the developers managed to remediate it.
As most of you know, PZ has an issue with zombies flashing green just long enough for you to swing, only for you to miss because you were only just within lateral range of your target and sidestepped for a fraction of a second.
In the early days of Team Fortress 2, Spy had a similar problem. When behind an enemy he was in the range and able to backstab for a one-hit kill, his knife would play a signature animation where it would raise and point down ("ready for a backstab"). However, like other classes, there was a (0.25 second) delay on his swing animation, before the backstab would check to see if the spy was still in angle and distance. This led to a horrid number of 'failstabs' and frustration on the part of players who felt cheated out of a hit, when the animation would play but the enemy would turn away just enough to turn it into a regular hit. Spy is a notoriously weak character whose main strength is the ability to backstab opponents; if he fails to backstab, he will almost certainly die immediately to any other character. So, while tightening up some netcode around latency and hitbox rollback, the development team elected to make Spy's backstab instant upon clicking:
What You See Is What You Get. This change has never been reverted.
I recommend TIS take a cue from this solution with swinging at zombies. If the zombie is highlighted green when you click, they should be hit, no matter how much later the swing comes. This might result in some janky-looking hits, but it's my recommendation that in matters of jank, the player should typically be given the edge; it makes little sense to rule in the favour of a computer-generated opponent that might come by the hundreds and against a character that may encompass hundreds of hours of effort, and has not made an obvious mistake to punish. On a personal note, I will always prize reliable gameplay systems over how a game looks.
If realism is a concern, I contest that if you were attempting to hit a person with a baseball bat, effectively doing so may be difficult but landing a hit at all would likely be nowhere near as stringent as PZ generally treats it.
I suppose that wasn't as brief as I thought it'd be after all.