I think there should be more survival aspects be taken into concideration for balancing the Game. Just more Zeds isnt the right recipe imho. Durability from clothes maybe in Cold Climate so you have to look for more. Maybe harder to gain loot or lots of stored Foot maybe attract Zeds and overrun your second Safehouse where you stored it. Maybe Zeds smell you better sometimes, or noise made could made more of an impact. A more unpredictable Zombie Routine should help too. Maybe Zeds following you longer and you have more Problems with endurance and just cant outrun every Zed that make Looting often very easy. My toughts on the Topic. Just more hack&slay wont do the trick to me.