It's the bolded stuff: Why did some of them become useful NBA players and others got scrub roles? If the NBA vs Euroleague relationship was as linear as you make it sound, why didn't double figure NBA scorers stand out in the Euroleague more than NBA scrubs/bench warmers?
To put it another way, there's a big difference between a -17 and a -5 margin.
Out of those 5:
Stojakovic was very young, if he play during his prime in Euroleague he would average 28-30 ppg. Hell, he scores 21 ppg and was just on rookie Nba level
Danilovic comes in the NBA when he was Top 3 player in Europe, the year he won the Euroleague scoring title he won also his 3rd consecutive italian championship while scoring more than 27 ppg if i remember exactly. At his peak, he was a solid NBA player. We have seen both peak Danilovic in NBA and peak Danilovic in Europe. I love the guy, too.
Smith: well, he was just not too good to play more NBA minutes.
He try multiple times, before/after Europe, but he never made it.
Kleiza comes at his peak as a Euroleague scoring champ, he was on a very bad team and he manage somehow to score 10 ppg...still, a solid NBA bench player, nothing more.
Navarro instead was a top player in Europe, i say top 5, and i personally believe that his style of play very well fits with NBA style of play. Thats he still have a good season but not losing just about 6-7 ppg from his former eurloeague champ year