Interesting point but I'm not sure I agree. There are other professional soccer leagues in the UK aside from the Premier League as well. It's not entirely apples-to-apples because the wider market structures are different between the US & UK, but I do think comparing the dominant player in each market is useful & instructive.

I think your point is totally fair though in that my description of NFL as a monopoly isn't as comprehensive as I expected. From what I can find, CFL revenues are about $213M , and US college football is $3.4 billion. CFL is pretty close to being a rounding error compared to the NFL, but college football is a definitely a significant presence. I think I'd say a market where one entrant commands almost 80% of the revenue is pretty close to being a functional monopoly, but not entirely, so I should have accounted for that.

And the CFL as well.