I generally agree with this. When we look at the good fighters from each region they tend to fit this pattern; the US has an extensive wrestling & boxing scene and almost all their top MMA fighters are wrestle-boxers of some sort, UK has boxing, kickboxing, and Muay Thai so their MMA fighters are mostly strikers, Brazil is more kickboxing & BJJ so their top fighters are a mix of kickboxers & BJJ artists, and in the former Soviet nations it's gonna be Sambo fighters, wrestle-boxers, or wrestle-kickboxers depending on the region.
An organized system for martial arts & combat sports means you can get everyone learning & competing from a younger age, and it also provides a lot more opportunities for training, competing, and getting good. If I wanted to start training for MMA here in Canada, I'm pretty much shit outta luck if I need to train wrestling, I can get some decent BJJ and boxing/kickboxing but finding a good wrestling or Muay Thai gym is really freakin' hard.