Look I am not sure who was a better shooter but there is a clear difference in approach in European basketball and the NBA. People think that the teams are more oriented to stars like they are in the NBA. This is quite often not true. Teams in Europe are built to play team game and in a lot of ways be an equal opportunity offense. Of course there are exceptions as there will be more plays called for more established stars.
Young players, unless they are playing on a team known for developing young players and giving them big responsibilities (e.g. Mega) they are played as role players, no matter how talented they are. Frank is 18/19 years old. For a team not known for their player development, he is not going to get many shots. Bogdanovic was the most talented youngster at Partizan when he was 18 but he was riding the pine more often than not and did not get many opportunities to shoot and this is for a club that is well known for player development throughout Europe.
I think Dennis Smith Jr has the higher ceiling, and certainly the ability to contribute more quickly from season 1. Smith Jr is a scorer who's highlights show he's also a talented passer and a capable shooter. You look at the highlights, what sticks out for Smith Jr is his lack of fear to mix it up on drives to the rim. He is not afraid to attack and finish. This may be a bit hazardous for him injury-wise in the NBA, but I would be very pleased if the Kings drafted him. He's undersized, but he should do well. Now Smith's defense is his weakness although it looks like he had some nice steals in highlights, and where Ntilikina gets the nod at first. I'd much rather get a confident NBA ready guard who wants the rock to the rim rather than a younger Talented European player who will need more development time.