Well argued, with the caveat that I doubt anyone really thought Rousey could beat a trained male (even Rousey put it in terms of "never admitting defeat" rather than thinking it likely). In judo barely top 500 men from lower weight divisions would throw her around like a doll in randori (practice); the difference in speed and strength between men and women is too much when you get into the trained end (though Rousey would throw around untrained men her size easily). I think those statements my Rogan etc were to hype the product, not something they really believed.
However, many did think she was the greatest WMMA fighter, and in that light your right, Cyborg-Rousey would not have been a freak show for those that believed. But I don't think that includes that many people, probably including Rousey herself. She's smart enough to know the difference weight makes (for instance, heavier international level women in judo - and Cyborg would be a full weight division heavier than Rousey with same day weighins like in judo) easily beat Rousey all the time in practice. Rousey is an excellent self-promoter, but she's not a moron, she was very well aware of what happened when she went against heavier women in judo - why would she expect anything different in MMA? There's a reason for weight divisions.
I notice that its mainly boxing and MMA fans who expect champs to go up in weight. In most combat sports there's no such expectation. For instance, look at any of the "greatest" Olympic wrestlers or judoka, people like Satiev in wrestling or Nomura in judo won three Olympic gold medals at the same weight without anyone saying their refusal to go up in weight for the next Olympics was a mark against them ... in fact no one in judo or wrestling would even think to suggest it, because its well known how important size is. You'll never find a comment on a wrestling forum saying that Satiev should have gone up in weight for subsequent Olympics; instead he's regularly listed as the greatest or at least top three greatest wrestlers in history. Rousey comes from that legacy, and going up in weight for the challenge is considered kind of daft; you go up in weight when your body grows, not because you won gold already and need a new challenge.