Please, do write out a proof
You're acting like what you're suggesting is a completely new feature
Let X represent the complete game as it is now, and let Y represent a new feature to the game. let Y=0 represent the new feature altering absolutely no other features in the original game whatsoever.
X+Y is the new composite game, Whenever Y is 0, X+Y = X. If the player has the ability to set Y= 0, and the player wants Y=0, then they will always have X.
Coalitions are not a feature that can be ignored completely without changing the game and as such are not an applicable example. I am not asking anyone to play suboptimally.
The original point is that you are arguing against is that there can exist a feature that people who WANT to play without (who desire to play suboptimally as you put it) can play without it and have the current game be entirely unaffected by it. As you put it, it is tautologically true that if a feature exists that you can ignore completely without altering the game, you can experience the exact same game you currently do.
I did not propose a feature recently in this conversation, although I have proposed several that qualify as an entirely ignorable feature (such as backwards version access). Another option would be a game start option to turn on the difficulties you currently desire, A third category would be player only options such as the PU CB being returned to its original state in single player-I don't actually like this last idea, but since the AI doesn't use it, it doesn't alter the game in any way unless you chose to use it so it qualifies.
Obviously many suggestions don't qualify as something that is completely ignorable, but if your goal is only to have the current exact experience and you don't want anything new, you are in luck, just make a backup of the current copy and laugh at the misfortune of anyone who wants an older version.