Regarding sports, Boxing is unique.

For example, despite a much larger global population, there was more Boxing matches per year that now during the mid to late 1920s(Dempsey), early 1930s, and the mid to late 1940s(Louis).

Early records are incomplete, but there is stats that over 27 thousand pro bouts did happen in 1931.
Nowadays, despite a much larger global population, we have about 20 000 pro bouts per year.

In the early 1980s Golden Age (Hagler, Sugar Ray Leonard, Hearns, Duran), there were about 12 to almost 15 thousand pro bouts per year.

The point is Joe Louis ruled the roost for 12 years and 25 Title defenses when there was far more Boxing than now, and what Joe ruled over has now been broken up into 2 weight classes.
1946 (Louis/Conn) has over 28 thousand matches that year.

David Haye is a world class fighter and has accomplishments, but they pale in comparison to the Great Joe Louis' accomplishments.

I think Joe Louis is the most fundamentally sound Heavyweight Champ in Boxing history.
Physically, they're about the same size. Louis carried his power late into fights, didn't gas out.

Haye is not very slick at all. He has very fast hands though.
With a better Coach to refine him for the top levels, Haye could have added more tools to his arsenal, the potential was there. Like how Roach refined and developed Pacquiao further. Like what Emanuel Stewart was able to do for Lennox and Wladimir. In Haye's entire career, he hasn't fought anything like what Joe Louis was.