Dude, trust me, Papaloukas is better than JJ Barea! Kill Bill is obviously very biased when it comes to Greek players, because he is Greek himself.
However the Euroleague is very very tough compe ion. No college team would come close to sniffing a win against any of these guys. I have no doubt that Papaloukas, just like many others, would have had a good NBA career if he came over early enough. However not everyone dreams about playing in the NBA. The economics have changed.* Top Euroleague players make more money than the NBA MLE, especially considering the weakening of the dollar compared to the euro. Not everyone wants to take a pay cut for 2-3 years, before he can get a bigger NBA contract. That is why guys like Javtokas, Diamantidis, Papaloukas, Smodis maybe, never come over to the NBA. That is why Dejan Bodiroga who was the best Yougoslavian player of the 90s (yes, including Divac and Peja) never seriously considered coming over to the NBA. They were treated like gods, made very good money, no need to give that up.
*There was an article by Hollinger, who is an econ grad, that explains very well some of the changes in economics that are happening right now. Hollinger actually argued, that if the league keeps pushing the age limit to 20, it would make perfect sense for the top high school players to go to Europe for 2 years. They would make money, AND receive much better coaching than they would in ty NCAA play. It makes perfect sense actually. The only thing is that there would be a cultural barrier of sorts for 18 year olds to go overseas, however Europeans do it when they come to the NBA. No reason Americans can't get adjusted. Plus it's not like living in Rome, Madrid, Athens is actually a bad thing. No way living in college can match that.