While your point is valid, that is not quite what I have in mind - you could technically step away with the zombie, keeping it in your range, but it wouldn’t be able to hit you.
That is actually a technique people already use in CDDA, but with a small, fast weapon. They wait for the zombie to come to them, attack it and step away before the zombie can hit the player, they repeat that and voila, a dead zombie without any problems.
The same technique with a longsword/zweihänder/spear(or in general a long melee weapon) would be that you have a certain reach and can attack the zombie for longer without it reaching you - when it finally reached you, you can step out of the way and do it all again - The speed of the melee weapon would lack, but the Reach would make up for the fact, essentially enabling you to do a similar thing to the fast knives.
I have to say though, this would be gamey to some extend, and I don’t have the feeling it’s a good idea to implement it this way. Still, would be an option.
I agree on the other hand with Random, the higher chance to hit would also work out.