This is not a zero-sum game. CDT does not outperform TDT here. It just makes a stupid mistake, and happens to pay it less dearly than TDT

Let's say Omega submit the same problem to 2 arbitrary decision theories. Each will either 1-box or 2-box. Here is the average payoff matrix:

• Both a and b 1-box -> They both get the million
• Both a and b 2-box -> They both get 1000 only.
• One 1-boxes, the other 2-boxes -> the 1-boxer gets half a million, the other gets 5000 more.

Clearly, 1 boxing still dominates 2-boxing. Whatever the other does, you personally get about half a million more by 1-boxing. TDT may have less utility than CDT for 1-boxing, but CDT is still stupid here, while TDT is not.