As some who has to get work permits in 2 different countries, and have friends who did in 10, I can testify that British immigration system is one of the most difficult, arbitrary and expensive, far supassing Spain, portugal, Germany, Czech Republic, Canada, Mexico, Brazil, Ireland, France, etc
The only immigration system I am aware of that's more hostile is US.
Obviously there are many countries I know nothing about
I'd think that's an outlier experience. Clearly it depends on various circumstances and there is a more of less hidden institutionalized racism involved, but as a German, immigrating to USA was smooth sailing (via green card lottery in my case).
More important however might be the interaction with locals. And from what I witnessed, Americans (well, Californians at least) are much more welcoming than Germans.
How many people do you think live in the EU? Because the largest countries (China and India, respectively) 'only' have about 1.3 billion people each, about 3x the EU at 450 million. Even the entire rest of the earth combined won't get you to "north of 20x" that number.
The only immigration system I am aware of that's more hostile is US. Obviously there are many countries I know nothing about