I figured somebody would make a post on this by now, but guess not.
So lets start with Zombines. If you have any kind of gun + speed perks, they arent the end of the world (usually.)
But as melee? You get absolutely rocked. My concern isn't their speed, or their health; It is their INSTANT swing.
When fighting bots especially, you have a very high chance to get hit every time you melee them. (Its even worse with player bots, due to latency.) You can't dip in, hit them, and dip out while they are getting knocked back a bit. Any time you go within their range, they instantly hit you like 70% of the time. This is quite ridiculous and unfair to melee mains. You can't listen for the audio cue and counter/dodge it, its just busted. Even aesthetically, the Zombine is just a zombie with armor on. Why would having combine armor suddenly allow you to swing that fast? I highly suggest you change the Zombine's melee delay to be similar to a regular zombie.
Lets talk about Fast Zombies and Lacerators. I've played multiple different zombie survival servers, and I have never seen a lower leap delay then I have on here. People play fasties literally just for leap spam, hardly ever using the melee.
This is especially strong against melee, since you can hardly hit them while they leap at you. (10 damage every time btw.) You have to hit an incredibly precise midair swing, using a long reach weapon (70 - 80 range.) Bots will always leap exactly where you are going unless stopped by the navmesh somehow. This is incredibly annoying, and also unneccesary. Fast Zombies and Lacerators have M1 for a reason, they should be using it.
I suggest that you increase the Fast Zombie/Lacerator leap delay to 2 - 3 seconds, after they land.
Neither of these changes would affect the zombie team too much, while making melee actually able to fight wave 5 zombies.