Let's say Knies hits his potential, which some people put him as a Blake Wheeler type. And let's say Wallstedt hits his potential, which I know is lazy but Lundqvist. I wouldn't trade Lundqvist for Wheeler.
Honestly.. that's not such a cut & dry thing either.
Sure, in isolation you can certainly say that Wheeler has more value than Lundqvist, but if Winnipeg already has Hellebuyck, then you're probably not doing that deal...
And therein lies the challenge. Goalies can either have immense value to the point of being untradable (the true #1 guys), or they're backups, and sort of a "who cares" approach.
If Wallstedt develops into what everyone thinks he's capable of, he's untouchable... but if he stops a little short of that, he's just reasonable tandem goalie and guys like that are very easy to find and replace.
Knies may not turn into Blake wheeler putting up multiple 90 point easons and a bunch more in the high 60s to mid 70s... but even if he's a guy that's a consistent 60 point guy who occasionally gets into the 70s; he'd still be a very valuable player.