We are not being dishonest here. Even if Born's rule was postulated, WMI would still have the most technical merit. Physics can never have a proof anyway. And

We are not being dishonest here. Even if Born's rule was postulated, WMI would still have the most technical merit. Physics can never have a proof anyway. And the Born rule is just assigning probability to the norm-squared of the wave function, so I'm not sure why you think it's assumed in a derivation of the Born rule itself. That would make the proof a tautology. The assumptions are laid out explicitly for the various proofs throughout the series of papers and critiques. QBism is all about belief of agents and if you think that's a valid approach than the decision theoretic proof from Deutsch and Wallace shouldn't be hard to accept. Actually a derivation of the Born rule in QBism must take the same form. A superposition of two different states is two copies after decoherence. They occupy different parts of the wave function and they share nothing, so can't interact. In configuration space (not classical space) they are separated "wave packets".