More comments on this particular objection:
I don’t really understand how this statement is significant at all. In our simplified picture, indeed, initially, the amount of MI is at maximum: the three circles overlap each other perfectly. But I don’t understand how this proves anything about CMI. As I showed in my explanation above, the only way you can object to Josh’s argument is if this you can lay down mathematical rules for how fast the circles can move away from each other. But simply saying that initial MI is needed doesn’t say anything. It does not restrict the movement of the circles.
Indeed, the rules of the movements of the circles is something we can only study in the lab, and if Josh is representing the biology correctly, then we do have good explanations (e.g. common ancestry or selection pressures) for why the cancers, for example, move in coordinated ways.