Tactical context is indeed matters, mate. Sometimes, the tactical hides the actual level of a player...it can be good or bad.
And also the football style and environment will affect the player.
Kagawa looked a very weak in EPL, same with Mkhirtayan. Both of them on of Bundesligue best. They could not cope maximally with EPL.
Javi Martinez, remember him ? The one who thinks he was WC and could play for mighty Bayern, so he bought his own release clause. Where is he now ?
Gotze, not praised as Dortmund wunderkind but also German wonderkid, what happened to him now ?
Or Messi in Argentina as an example.
Young player being good does not mean he will be a WC in a sudden. Martial as an example.
And being USA player, the king country of Marketing gimmick (remember Addu ?
Altidore ? Bradley ? Clint Dempsey ?) but with no strong root in football, how can you expect a WC talent has been born ?