Hedman is a really good example. He wasn't great his first few seasons and then it all came together for him.
I was in the small (tiny) camp that believed in Ceci while he was a Sen. After watching him this past season with the Leafs, I've officially given up hope that he'll become a top four d-man. He definitely struggles with the speed of the NHL game.
AS for Lassi, he has speed and a great shot. I think he probably takes way too many risky chances right now. He'll have to cut that out but he's undeniably talented. I watched him at the Sens development camp in 2019 and his moves brought people out of their seats. We'll see.