In these recent discussion about Biles, I've seen this exact conversation a few times. People say that gymnastics organizers need to keep it competitive to have audiences, and people disagree and say the organizers shouldn't worry about that. They should worry about fairness. This implicitly accepts that a dominant competitor at the top level decreases viewership.
Is that true? I don't think so. And, I think there's lots of obvious evidence it isn't. Did people stop watching swimming when Phelps was dominating? No. Did people stop watching cycling when Lance Armstrong was dominating? No. Those sports had a huge increase in viewership, at least in the US where I was at the time. It's not even limited to the home country. I certainly hear more about sprinting after Usain Bolt than before.
If we extend to team sports there are even more cases. Remember when everyone around the world stopped watching NBA basketball because of Michael Jordan and the Championship-Era Chicago Bulls? I sure don't.
So maybe gymnastics is totally different, but that seems odd. I can pull examples from local sports, worldwide sports, team sports, individual sports, big money sports, small money sports, fighting sports and even auto racing. There's nothing about gymnastics that seems different from all other sports.
Maybe this is an unsatisfying conclusion, but I don't know why people keep thinking this, that you need evenly matched competitors for the audience. There are people who keep commenting it, and the judges act like it's true. And maybe an upsetting conclusion to some, but after writing out this whole comment I can't come up with a better answer than "she's a Black woman". So maybe that's it.
If someone can name a case where a dominating competitor decreased the popularity of a sport, I'm genuinely very interested to hear about it.