You're treating resources as one single kind, where really there are many kinds with possible trades between teams

I think this is reasonably realistic. Let R signify money. Then R can buy other necessary resources.

But my point was exactly that there would be many teams who could form many different alliances. Assuming only two is unrealistic and just ignores what I was saying.

We can model N teams by letting them play two-player games in succession. For example, any two teams with nearly matched resources would cooperate with each other, producing a single combined team, etc... This may be an interesting problem to solve, analytically or by computer modeling.

You still haven't given good evidence for holding this position regarding the relation between the different Uxxx utilities.

You're right. Initially, I thought that the actual values of Uxxx-s will not be important for the decision, as long as their relative preference order is as stated. But this turned out to be incorrect. There are regions of cooperation and defection.