I believe a better way to balance would be to be a little more lenient with exhaustion yet increase toughness of zombies. One of my most fun playthroughs were with insane tough zombies. This alone meant that I couldn't simply go anywhere and fight my way through it but that I had to carefully choose my fights and retreat when there were too many to fight since taking on more than 5 without splitting them was pretty much a death sentence. It could be seen as tedious sometimes but I had a blast. In my opinion, melee combat as a whole could use a rebalance. A player character without any fighting skills should not be able to take on several zombies at a time. Although exhaustion working as a cap to the player fighting ability is nice I think that either swing time should be increased or mobility should be reduced while swinging. Of course damage could be increased to make every swing more important instead of mindlessly mashing the same button hoping the zed is dead. I think that this alone should mean that people wouldn't be able to consistently take on several zombies simply by running back and hitting. After all there isn't much ground in general pop culture zombie lore for this kind of behavior. For example I've never seen a zombie movie where characters simply run back swing then run back repeteadly to trim a horde.
