Sounds like you just need to work on swinging horizontally, no offense. It's not any harder. If anything it's easier. You just strafe sideways and aim up a little and it turns one headshot into 3. The only time you should use the vertical attack is if you are in a narrow hallway and you can't strafe past along the side.
Also you completely ignored the part where I said support can kill a 6 man HoE scrake in a fraction of the time that zerk can. I'm using it as an example to compare damage, not as a common scenario. It takes 2 or 3 alt fire shots from the boomstick to decap a scrake and then you just run away and they die. Meanwhile the zerk is dancing circles around them for a full minute, knocking them all over the place and going through more than 2 mags of pulverizer ammo to do the same damage. I don't expect zerk to kill at the same speed as KF, but at least put us on the same damage level as support if you are making us use melee attacks.
The point is that they nerfed the hell out of zerk in this game to the point where he really serves no purpose anymore. You would always be better with another medic using a pulverizer or AA-12.
Horizontal strikes are not always better on big zeds or even small zeds that you stumbled (especially gorefasts) when you need to score a critical headshot.
I hope they do not EVER make Zerk do as much damage as Support. Support is a damage dealing class, which Zerk is not. Zerk is a damage MITIGATION class. This is true for the whole team. The Intimidate perk is a typo, it actually makes Zeds do 25% less damage for their lifetime.
On top of that you have more tools for stumbling Zeds or preventing rage than any other class.
Taking another Support or Med is not a good choice over a talented Beserker that uses his EMP grenades. Beserker is the nail, he keeps them busy and buys time for the team, stumbling Zeds about to hit teammates or parrying to get a little extra time when an EMP takedown goes bad. Support is the hammer, he supplies the massive damage while the Zerk subdues the Zed.
You can solo things as Zerk if you're very skilled but it's just not what the class does anymore.
Medic is not a better Zerk because that means you have a Med not healing at crucial moments and he also has no damage reducing perk or stumble increasing perk. Med can also be grabbed by Zeds. Not to mention you lose the insane melee swing speed and damage bonuses. You literally are only able to Stumble with the Pulv alt-fire and Parry (which you usually wont have it out as Med meaning you are not as prepared as a Zerk). Just because you can still right click Stumble a Scrake as Med doesn't mean Zerk is instantly useless.
You're way better off having a skilled synergizing Medic/Beserker player combo
with a few Supports and Commandos mixed in there. This has been a winning team nearly every time with decent players.
Good luck finding a game with Supports who can pull off a 3 shot Boomstick kill when your team is down in the thick of it. No game has optimal conditions the whole time and that is largely when Zerk can shine. You have control over Zed's movement and you can mitigate their damage like no other class.