Good points, but there are just as many young euros that make it after coming over, after getting drafted.
Porzingis, Dirk, Pau, Marc gasol, Andrei kirilenko, zdrunis Ilgalskas, vlade divac, to name a few.
The problem is that once they get too comfortable in Europe, a lot of these player never come over to the NBA and you waste a high draft pick. I would rather he learn in an NBA environment, even the d-league would get him more used to the NBA speed than a euro league experience.
Even if he has to spend a year in the d-league, I think vlade and the kings would prefer he be in America learning the game.