I 100% get where you are going & you obviously know prize fighting history so props.
But it is actually the exact definition of "sport"
sport
spôrt/
noun
noun: sport; plural noun: sports
1.
an activity involving physical exertion and skill in which an individual or team competes against another or others for entertainment.
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Most major sports have adapted rules that screw with tradition & what is fair to make more money
Look at the playoffs in NHL, NBA?
Sometimes under 500 teams get in playoffs.
Look at MLB ... they created inter-league play so Yanks/Mets can play each other & have 6 sell-outs
It is not as blatant as boxing/MMA, but its about the money
You don't think MLB is happy the Yankees are a WC team even though they are 10 games out? Of course they are ... that is why they allow second place teams to have a chance to win WS
In the literal sense and by strict definition, boxing and MMA are "sports", 100%. Boxing is even in the Olympics.
I'm talking more so in terms of public perception and operation. In that sense, I would argue boxing and MMA are more closely related to pro wrestling than they are to the NBA, MLB, and other mainstream sports. There are always concessions and changes that mainstream sports leagues implement to maximize revenue and make the sport more appealing to the public, but as you alluded to, not nearly as drastic and blatant as in boxing/MMA.
For example, if the Red Sox and Marlins made it to the World Series (not sure if that's even possible, not a big baseball guy), MLB wouldn't get together and say
"listen, we can make WAY more money if it's the Red Sox vs Yankees, so let's book that instead." Baseball fans would riot. It would kill the company, even though more people would rather see the Yankees than the Marlins, because baseball fans care about the integrity of the game and without that integrity, the league suffers massive loss.
Yet that happens all the time in boxing and the UFC. Ratings seem nearly pointless and titles (even if they are interim titles) are taken away on a whim with no explanation needed. Nobody really cares. Nobody is going to riot and boycott the UFC if Brock Lesnar comes back and gets an immediate title shot. The UFC profit greatly from shoehorning Lesnar into a title shot, or a near 40 year old pro wrestler with no MMA experience onto the main card of a PPV. They're not valued as legitimate sports by most, they're valued as a spectacle.