I don't know honestly I think it's American training that sucks even though we have the biggest best gyms and resources we still don't use them properly.
You can see this in the MMA video games there are more foreign names then there are Americans.
these are the people who over the long-term have dominated mixed martial arts in America
despite having all the resources in the world we have the worst training because it separated it into monetary income streams ( multi martial art gyms cafeteria-style rather than straight mma from day one)
If you take two identical twins and one trains in Brazilian jiu-jitsu wrestling and Muay Thai and the other one straps on a pair of cage fighting gloves and trains nothing but MMA from day one the MMA twin is going to monster Mack the multi-disciplined twin.
Russians had combat sambo,
Brazilians had Vale tudo/bjj
Japanese had shooto
All we had were a few wrestlers in the beginning, remember the first few UFCs...the USA got SMOKED!!!
GSP
FEDOR
Silva
Aldo
Gracie
Sakuraba
Rutten
McGregor
Khabib
Velazquez
Dos Santos
Rua
List goes on and on
Plus we're not talkin about exclusively the UFC we're talkin about MMA worldwide...
However UFC alone=
68 USA
30 international
Championships...
Nearly half of America's largest MMA championships have been dominated by non-americans that's some pretty amazing data!
And three out of five of the longest reigning ufc championships are Anderson Silva, GSP and Jose Aldo!
https://en.m.wikipedia.org/wiki/List_of_UFC_champions
Pretty sad performance considering we invented modern mix martial arts competition as it is known today!