I hope he's better than Marion. I think Shawn Marion was one of the most overrated players during his time.
I think it's more the other way around.
He was in the shadows of Nash and Amar'e (he was essentially the forgotten man on that squad), and because the Suns weren't a great defensive team that marred his reputation as a defensive player, which is why he didn't even make one All-Defensive team, which if he was playing on a team like the Spurs, he would've had at least five of those badges.
A prime Iggy is probably an apt short term comparison of what Kuminga can become on this team. Long term is a bit more difficult given he's going to need the ball in his hands to really become a star, and I don't know if this system will allow that to happen.