Interesting post, although I'm not sure I totally buy your theory. And here are two examples from both a male and female perspective.
Pete Sampras, in his glory days, was certainly not embraced by fans or sportswriters, who basically decided he played great tennis but wasn't very interesting. Really, it's been in his later years, especially during his struggles, that the fans and the press have taken him to heart.
No one has ever accused Chris Evert of not being feminine. And yet, in her glory days, she was not the fan favorite. She was thought of as cold and calculating. Bud Collins dubbed her the "Metronome Queen." It wasn't until that Chris began losing matches that the fans embraced her.
Ditto for Monica Seles. In her younger days, fans and especially the press did not care much for Seles. Once she was stabbed and returned to the tour, however, she became a crowd favorite. I don't think it's because she is a woman though, but rather that she is viewed as a tragic figure and people sympathize with what she endured. Had a major male tennis player had the same thing happen to him, I think the results would be the same.
Another case in point is Jimmy Connors. He was reviled in the early days of his career and people enjoyed seeing him lose. By the end of his career, he was considered THE fan favorite.
Now let me tread carefully here because I don't want to offend anyone. First, I am not a fan of Venus or Serena. It has nothing to do with their race or their gender and it has everything to do with my early perceptions of both girls. My early perceptions were very negative because of what I perceived as arrogance and conceit and an extreme lack of professionalism. I gladly admit that I no longer carry many of these perceptions about Venus and Serena. In fact, as someone who genuinely loves tennis, I happily admit they have raised the bar in women's tennis. Serena and Venus are in a class by themselves. And while part of me relishes their rags to riches story (It's the "American dream" in reaility, although I don't buy into all that much as they were millionaires at age 12 or so!), another part of me just can't overcome those early perceptions.
Are Venus and Serena making the game boring? I don't agree with that -- it's too easy of an explanation, the converse of which could just as easily be that the rest of the tour is making the game boring because they aren't keeping up with the Williams sisters. Venus and Serena simply have raised the game to a new level, and the other players don't have the goods to match them. The problem, from my perspective, is that unlike past rivalries between say Chris and Martina or Steffi and Martina or Steffi and Monica, etc., there is no contrast of styles when Venus and Serena play each other. And although some may take exception to this, with the exception of this year's Wimbledon final, the two sisters simply haven't played a great match against each other. In fact, remove the hype of their sister act, and there really hasn't been anything to get inspired about. Compare that to the other great rivalries in the game, and you can get some understanding as to why people are disappointed by their matches.
And by the way, golf is not a sport! And golfers are not athletes! Hey, it's one man's opinion!