The bolded is not true.
1) The most transcendent periods of the NBA, MLB, and NFL were, arguably, during dynasties. The Celtics, Lakers (2X), Bulls, Heat, Warriors, Yankees, Red Sox, Steelers, Niners, and Cowboys all were ratings and revenue booms for their respective leagues. For example, look at NBA ratings since the Warriors Dynasty disbanded even though the NBA is the most wide-open it's ever been in the last decade.
2) Competitive professional sports are too cyclical to have any entrenched dynasties. Outliers happen enough in ownership, player development, and coaching that it is extremely difficult to stay on top. Similar to how only 60 of the 500 U.S. fortune 500 companies in 1955 are still on the list. Shite happens.
3) The only reason why U.S. sports leagues exist is that they have federal anti-trust exemptions and their employees must be allowed to unionize. I would assume it would be more difficult when dealing with an entire continent.
4) Do you honestly believe football would have grown in popularity in the U.S. and other countries if it wasn't for the media exposure given to the dynastic teams in Europe? The mainstream media doesn't care about parity. They want narratives.