To be fair, in the real world there are tons of athletes who aren't the "best" in their own countries but are still better than most from other countries, so they move/claim nationality for another team and play anyway.As opposed to the other tournaments not called World Cups where only players from some countries are allowed?
A world cup is a tournament between national teams, that is the definition of a world cup. I can't believe this is still in debate.
For instance, just a quick google yields as a top result: https://www.givemesport.com/1560083...nal-allegiance-and-played-for-another-country