I don't think we disagree on all that much, from your post. I agree that the MLB on-field product isn't great, but the league still has star power which sells merchandise (Aaron Judge, Giancarlo Stanton, Clayton Kershaw, Yasiel Puig, etc.) I think we're in agreement that NFL is declining. It'll take a while for any sport in the US to surpass the NFL (if ever), but WDW is a global attraction and NFL's attempts to expand beyond the US have been pretty lackluster, at best. No sport in the US has stars like the NBA currently does though. If any league was deserving of an immersive fan experience that would touch the greatest number of people, it should be the league that has been forward-thinking in terms of global marketing, VR experiences, and fan experiences during the game, not to mention a sport that isn't so dangerous that some school systems won't even allow it.
Don't get me wrong, just like everything new that Disney does, some people will be against it from the start. However, I think this one will be more successful than people realize. Just my $0.02.