It depends what you mean by "best players". Real Madrid have twice tried to just buy "Galacticos" - the generally-recognised superstar players - and cram them all into the same team, regardless of what position they were suited for. It didn't really work out like they hoped but it did get them a lot of attention.

They found more success when they bought the best team i.e. the best players in each position. Winning in football is difficult enough that you still need great tactics, management, experience, and luck to have actual sustained success. Money helps buy a lot of that, though.

But beyond Real Madrid your point is correct. More and more money is aggregating at the top, especially the English Premier League, and others are getting left behind.