What about as a distraction? If we've established that this clearly isn't the world outside, yet you've confirmed that we've vanquished the mastermind, then the natural conclusion is that there must be an unknown secondary force establishing the parameters of this scenario. You said it yourself in the beginning: out of one game "and into another".

Even if you refuse to concede that the other pieces on the game board might measure up to your own aptitude — a conclusion which may or may not be correct, but that we can assume here for the sake of the argument — that still doesn't mean they're entirely without value. They might provide useful information or prior experiences from which you could learn and make strategies. They also might facilitate your own ends, assuming you're capable of positioning them in such a way to achieve that. To say nothing of the fact that your behavior toward Genocider demonstrates clearly that you are aware of the advantages of numbers, assuming the numbers are well-controlled and work in your favor.

And if none of that is enough to content you, then there still remains the point that adding more variables to a situation fairly guarantees added complexity, and I can hardly imagine Togami Byakuya-kun turning down the opportunity to make a game more interesting.