I think Klefbom can develop into a bona fide #1. He doesn't have franchise D potential like those you listed obviously, but Klefbom has legit #1 upside.
Klef needs more PP time and he needs to shoot more. To be a bona fide #1 you need to be elite in all 3 zones. I think we'll see more offensive production as he gets older and further develops his chemistry he has with a defensive Dman like Larsson. Both of them are only 23, and Dmen take longer to reach their peak but generally peak for much longer than forwards. Dmen can play at top levels well into their mid 30s.
Larsson reminds me a lot of Vlasic in the defensive zone. He's more physical than Vlasic, but Vlasic is a better skater and better in the offensive zone. Vlasic is in my view the top defensive Dman in the NHL, Larsson's gap control and defensive awareness in closing passing lanes, limiting prime scoring chances, and keeping forwards to the outside reminds me of Vlasic.