Something that bothers me about this tournament: I feel like a competitive tournament doesn't actually reward the kind of strategy that is meant to do well in Prisoner's Dilemna. As a (highly oversimplified) example, consider three bots who have the scores:

A: 10 B: 9 C: 2

Here, A is 'winning.' Suppose B can make a move that costs A 3 points and costs itself 1 point, leading to:

A: 7 B: 8 C: 2

B's payoff function has dropped. However, from a 'winning the tournament' approach, B has gone from 2nd to 1st, and so this outcome is now better for B. This feels wrong.

I doubt this was a really big issue here, but just on general principles I feel like competition by comparing scores is incompatible with a desire to explore the Prisoner's Dilemma, since you're turning a non-zero-sum game into a zero-sum game.