He's absolutely right. Especially the big mans. If you "can't play the game", you are going nowhere in Europe.
American bigmen: Big, athletic, bruiser, intimidator, but what about actually playing the game of basketball?
e. g. Andre Drummond is a super athlete, but the ball is crying in his hands, can't shoot a lick, why? He's just a way more athletic Kendrick Perkins.
American guards: super flashy, but they are playing for themselves, that's actually the easier to solve.
The biggest take away: skill-less american big men will have a hard time versus skilled (but less athletic) international bigmen. Especially if better athletes come out from Europe/South America.