Some top tier National Teams never reach full potential or get to find the right team chemistry in just a few weeks. Because of this National team competitions are lower level competitions than the Euroleague.
This is why national team competitions are rather unpredictable, since mediocre teams can surprise top teams. Teams like the Netherlands can almost beat countries like Croatia and Greece. Better yet, teams like Nigeria can knock out Greece in Olympic qualifiers. Teams like FYROM can even reach the Semi-Finals of Eurobasket, and I may even say that teams like Lithuania, who have the experience to find the right buttons in short tournaments, can consistently be medal candidates, while they would not even come close to make the Final Four in a Euroleague season.
There are a few national teams which can be EL title candidates, namely Spain or France among others, but these teams do not reach their full potential in short tournaments. When they do come close to their full potential, they usually beat other national teams by great margins all the way to the gold.
It is no secret that coaches have no time put their signature on the team in such a short period of time. If they did, then teams with the best rosters would be considerably stronger. The good thing is that the new qualification system will allow teams to glue and reach full potential in the final tournaments.