I appreciate the analysis you devote to these matches, especially to justify varied outcomes. You're right that small, agile women can have the edge on larger but less athletic ones. In a slightly different context, that's why little Ellen Page is believable as a roller derby star in "Whip It." As far as it goes, I'm quite happy to see the likes of Barbara Eden and Joi Lansing doing well here even though neither had a reputation as a brawler.
Personal preferences aside, though, I'm intrigued by what might have actually happened. All these women have actual histories, but it seems many voters remember only bits and pieces. For example, for all her sexiness, Jayne Mansfield was a creampuff who got demolished in a bar fight. Perhaps more illustratively, the Jane Fonda of this era was thin and not at all intimidating, so initially her success here came as a surprise. Pre-implants, Jane was flatter than any woman in this contest except Diana Rigg, so I thought she might be getting all the votes of those who prefer the small-breasted. But it seems more likely that voters remember the later, buffer Jane of her workout era, and credit her with retroactive toughness.
Conversely, Ava Gardner was well known in her heyday as a tough broad from a hard-luck background. Ava often got knocked around by husbands and lovers, notably crazy Howard Hughes and detestable George C. Scott. But it seems she often got in her licks. "I was six foot four before I married Ava Gardner," Mickey Rooney joked. Gardner also was known for her willingness to mix it up with the wives and girlfriends of men in her life. Similarly, Jane Russell was a physical specimen who might be getting some votes on the basis of "Hot Blood" alone. I'm not saying a well-toned, muscular, small woman could not beat either of these women, along the lines of the scenario you suggested. I'm just suggesting their overall fantasy performance seems to reflect considerable unfamiliarity with their real lives.
But that's just one opinion, and it's nice that you try to maintain neutrality.