The kid is still very young, he's growing and developing his body, and of course his game, but he's nothing like Gallinari.
Luka Doncic has more fight in one finger than most Euro wing prospects I've seen in a decade. The kid is a fierce competitor, and he would be more like a Paul Pierce than any other comparison. I'd like to see him staying with Real Madrid this season and two more, but I guess he'll declare in 2018.
If he keeps his progression, he could play 1-3 and only suffer with fast PGs on the defensive side. He's a strong rebounder, clutch scorer and there is no way you compare him to Gallinari:https://youtu.be/Dax24qnY9pU