Boxing as the one and only lucrative pro sport in the USA?

It's just for fun and a fantasy experiment. Thus, it doesn't matter if it makes any sense. Let's assume, an alternate history where boxing is the only popular sport in America.

There is no football, baseball, basketball, hockey, MMA, wrestling, soccer, athletics or whatever... Or they just play a minor role.
In short, I mean the talent pool is as big as the whole eligible population.
Boxing would be THE SPORT at every high school/college etc....

Comparing alternate history to actual history:
How much do you think the sport would have changed since 1900?
For instance, 3 scenarios:
1. Not that much.
2. A mixture between the known world class fighters and new ones.
3. It would be completely different. Even SRR and Muhammad Ali would be unknown today. GOATs would be others.

And of course how big could the change be at different times? Boxing used to be more popular in the United States than it is today. Thus, the differences might be bigger nowadays.

Maybe someone has some ideas?

BTW., I pick the USA because historically it is the greatest boxing nation (since 1900). The whole world would be too confusing. Who knows what hidden potential Africa, China, India etc. has...