... I would like to see zombies and bandits attack the player together on Horde Night (for example, from Gamestage 200) in the future. ...
Addition to my contribution before:
Take another look at season 8 episode 7 of "The Walking Dead" (the title is "Time For After"). The scenario that takes place there, you should create as a developer of the game at Horde Night.
People are trapped by zombies at "The Walking Dead" at headquarters. They can not fight the zombies effectively because their headquarters is threatened by ranged fighters (Sniper). Also, a truck is driven into the base to break the defense or the walls.
In their game the ranged fighters should be the bandits at Horde Night. If "Gamestage" increases, the bandits should use stronger weapons, they should become more bandits, and they should attack from different directions simultaneously. With "Gamestage" 200, shooters with crossbow can come first and with "Gamestage" 300 bandits with assault rifle and rockets. In the TV series, a truck is used to break through the wall. In their game, the bandits can use rockets for this purpose. These missiles should have less area damage but more damage for a breakthrough.
Ranged fighters will make the base building more complex, the fight more dynamic, and simple solutions will not work. The ranged bandits should fire and then change position a bit and then shoot again. So they are not that easy to hit.
The pure destruction mode of the zombies is the wrong way, because players then build a cube with side length 10 instead of a cube with side length 6. It is better if zombies (in several groups) try to hit stairs to get to the player. Then it does not matter how big the cube is.
A setting option, after how many days the Horde comes, is very important (7, 14, 21, 28, not at all). Then you can increase the level of difficulty of the Horde and who does not like the Horde, can make them appear less often.
(Unfortunately, I can only speak very little English. I have used translation program German - English.)