I think this is built out of several deeply misunderstood ideas.
If we get 2 AI's, where both AI's are somehow magically aligned (highly unlikely), we are in a pretty good situation. A serious fight between the AI's would satisfy neither party. So either one AI quietly hacks the other, turning it off with minimal destruction, or the AI's cooperate, as they have a pretty similar utility function and can find a future both like.
Nowhere does FDT assume other actors have the same utility function as it. Why do you think it assumes that. It doesn't assume the other agent is FDT. It doesn't make any silly assumptions like that. If both agents are FDT, and have common knowledge of each others source code, they will cooperate, even if their goals are wildly different.
With a high bandwidth internet link, and logically precise statements, we won't get serious miscommunication.