I don't think a lot of people understand just how good Doncic was in Europe last year. I think most people have the misconception that all the Euros that come into the NBA dominated in Europe and that is why they jumped to the NBA, when that is actually rarely the case. Most European players that come into the NBA are young prospects in Europe, and are often not stars are their own teams, let alone dominant players. Giannis was famously playing second division ball in Greece, Frank Ntilikina came off the bench for his French club; even Porzingis who was billed as being an accomplished player in Spain only averaged 21 mpg for his Spanish club, putting up an 11-4 on 49 percent shooting.
For Luka to be the Spanish League MVP and the Eurobasket MVP at 19, nobody had dominated Europe at that level before, so it's not surprising that he's doing so well in the NBA.