However, I have very little interest in whether 1 class is balanced against the other.
You could've stopped here.
Your absurd case thus does not sufficiently fulfill the criteria here, because, as I pointed out above, you can very well make the game itself challenging to a player who is using these mechanics, simply by making the game itself take advantage of them as well.
Complete non-sequitur. It's an internally coherent argument about the relevance of balance to cooperative games, increasing the complexity of the game does not negate either premise of the argument. You're begging the question.
It shows that balance is relevant to keep encounters interesting. In a PVP game, an encounter is between players and thus the balance of classes is what is important. In a game like solitaire, or any game where the enemy is not a player controlled character and all the classes are controlled by the player, the balance that matters is the balance against the environment. They are 2 different types of balance and your argument fails to show that you cannot balance a game against the environment by simply allowing the environment to also use the "broken toys."
What I will concede is that in an environment like that, if you balance solely around the top and not somewhere in between, it then becomes unplayable for those who only want to play with the bottom, but lets face it, even if the classes were perfectly balanced, they would not make a game which is challenging to people who are heavily invested into the combat because that would exclude the people who are bad at it. So yes, IMO a system with more depth, which is balanced around using surfaces to some degree (but not an extreme abuse case) is more interesting than a game with no surfaces at all.
And on the subject of world verisimilitude (in the event someone brings this up), how exactly is it believable that someone who can manipulate reality is "balanced" compared to someone who swings a sword. It isn't. In fact, it makes far more sense that a fighter is someone that is easily brushed aside by a caster. Surfaces are, in my opinion, far more "believable" than a wizard which is balanced in comparison to a fighter.
