I keep reading how people want the game balanced but what does that really mean. Most times I see players wanting some way for zombies to overcome the ways people have figured out how to survive without dying. When someone discovers a way to make a base super hard for zombies to breach then others want it fixed so the zombies have a better chance to break in. Then someone finds another way to keep them at bay and the cycle continues. One side has the upper hand then changes are made and the other side now has the advantage. To me balanced means the odds are even that one side will be still standing at dawn. You win some you lose some. To have one side always defeat the other eventually doesn't seem balanced to me at all. The point of any survival game to me at least is there has to be a chance you will die, but there also has to be a chance that you will not.
Fate is the ultimate game balance. To win all the time is hollow but to lose all the time is just as bad.
I hope I explained this alright. I am sure I botched it up somewhere but I am hoping some will know what I am trying to get across.
Great question.

I do think I know what you're trying to get across, and I'm happy to offer my perspective.
For me, balance in this case means insuring that the amount of time & effort you put
in is directly related to the amount of payoff you get
out. This manifests itself in myriad, often quantifiable ways. If you go mining for ten minutes, you expect a bigger haul than if you'd mined for one minute. A club that cost 600 Dukes should be demonstrably better than a club that cost 300 Dukes. Steel Smithing requires more to unlock than Concrete Mixing, so you expect steel to be better than concrete.
Anything that doesn't follow this relation is a potential cause for concern. For instance, if an enemy takes extra effort to kill, but doesn't reward you with more experience or better loot, then you'll stick to other enemies if you can avoid that one, and feel ripped off if you can't. Gazz likes to think of this as the player having "no choice" but to go for the other, more lucrative zombies.
So it is with the tower defense part of the game. If you or I ever reach a point where zombies can never reach us, we have acquired an
infinite amount of safety for a finite amount of effort. In the case of breaking a ladder, the time & effort put in for that infinite payoff is very small indeed. Your ladder+ramp technique takes a little more time & resources to make, but again, it sounds like something you can make once, and then never have to expend any more effort again. The output can't be reconciled with the input.
Before something can be balanced, it needs to be balance-able in the first place. Gazz can change the price of a club or the requirements for a perk, but there's nothing he can tune to make a broken ladder 10% less effective. Broken ladders exist outside the set of balance-able parameters, and that's not good.
Now, when I say that, some people think I mean ideal balance is when the player "loses all the time," but that's not it at all. First, broken ladders have to be brought into the set of balance-able things. That means it has to be
possible for the zombies to overcome them.
Then they can be balanced, by adjusting the frequency with which zombies grab chest-high ladders, or the speed at which they do so, or the types of zombies that can do this, like I said in the previous post. But everything needs to get in that set of balance-able things first, before the game can be balanced, which means the zombies have to be
able to overcome everything.
I agree with the idea of winning some and losing some. The right amount of prep time required to survive past the next horde night might be one hour, six days, or somewhere in between. That's a debate we can have. But my argument is at no point should that time & effort fall to zero. Wherever that happens, we have an un-balance-able situation. An out of bounds situation. An exploit.
Lastly, it's worth pointing out tower defense is only part of the game. You're framing it as either your base isn't breached, or you lose the night. But the close-quarters combat that ensues after that first breach is fun, too. I'd like to see that phase of the game become more recoverable, instead of the all or nothing, unscathed or death-loop-until-morning we get now.