You don't have to believe Sanheim could be better than Provorov someday, but the GM recently said that Travis is probably 4 years away from his physical peak. Do you think Provorov is 4 years away from his physical peak? Sanheim has a lot of room to improve. That makes him a riskier prospect than Provorov for sure, but a 20 year old defenseman with things to work on isn't always a bad thing. Especially when he's 6'4 and has the offensive resume that he has to this point in his career.
In comparison to forwards, defensemen develop at much different rates than forwards. That's why you find #1 D outside of the 1st round, yet not many #1 centers are taken outside of the top 15 picks, let alone the first round. If you look at some old threads of NHL players you will see posts of people talking in absolutes about teenage hockey players only to come back and look silly. Shea Weber wasn't supposed to crack the 1st pair in Nashville because they had Ryan Suter and Kevin Klein.