There are no guards on servers due to an MP bug that I THINK is fixed.
No zombies is due to hitting the max spawned zombies limit. Find this in your server config or control panel.
Code:
<property name="MaxSpawnedZombies" value="60"/>
Increase it to 100 to be sure, but 80-85 should also be fine.
Explosions through walls is a TFP issue, not a mod issue. Even cop puke can go through walls, or the explosion can hit you through walls. The second bunker is absolutely NOT supposed to be easy.
The behemoth is supposed to be hard. It's toned DOWN from the TFP version. Trust me, if you saw the damage TFP intended for the behemoth, you wouldn't complain (hint: Base 500 damage to a player).
So no. It doesn't need balance. It requires players to think about things.