,judging by the diminished popularity of boxing and the rise of other combat sports like MMA.
Listen, Yank, your country is not the whole world.
There's 195 other countries in the world, and 79 countries sent Boxing teams to the Olympics. Womens Boxing is in the Olympics now.

In the USA, Boxing may not be as big as it once was, and MMA is mainstream in the USA, but worldwide, Boxing is massive, and MMA is basically non-existent.
Boxing puts on 20 thousand pro fights each year, the main org, UFC, puts on only about 220 pro fights per year. And the paydays at the top of the respective sports are beyond comparison.

probably one of the last true greats we're going to see,
No. Someone'll come along.

Someone ALWAYS does.