Is this post brexit?
Spain will never be the best or biggest league, the individual TV deals sees an end to that, smaller clubs can't compete with Real and Barca because of the low amount of income.
It wouldn't for the next 3-4 years but after that there'll be a big drop off in quality, as it'll be British only players coming through. I'd comfortably say that 90% of the best PL players have been foreign, with barely any of them coming with a big reputation. So for the FA to turn them away if they got their way is ridiculous, the foreign players of the past have all brought different styles, skillsets, fanbases and character with them, those along with foreign coaches have helped mould the PL into the competition it is today.