You underestimate the reach of Messi. I lived in Italy for a large part of my adult life and had messages from friends there commenting on the Inter Miami replay which was being broadcast in a pub they were at. I don't personally believe the NBA comparison works well as you have global stars playing in leagues around the world - not just isolated to the premier league. A simple example is Mbappe is in France, Halland in England, Vinicius in Spain, and the heavy ballon d'or favorite in America.

The Inter Miami Instagram account went from under a million followers to one of the most followed accounts in American sports - beating every NFL, NHL, and MLB team.

I also think you underestimate how many people from the United States follow MLS. For example, Atlanta Uniteds 2022 average attendance was the second highest average attendance across sports in North and Central America. The 2022 numbers would put it at 8th highest average attendance in the premier league. The recent LA Galaxy vs LAFC match had an attendance of over 82k fans. For comparison, the 2018 Arsenal vs Spurs match at Wembly was played in front of 83k.

Also, MLS sees the heaviest growth around the World Cup time period. Over the next four years you have massive tournaments being played in the United States from the 2023 Copa America to the World Cup.