For what it's worth, Adam Larsson was looking like a question mark when he was only 21-22. He had already played almost three times as many NHL games as Mueller had, by that point.
Larsson is massively overrated by some people, he was also very underrated by people just 2 or 3 years ago. I think Mueller could be better than Larsson in a couple years, or maybe he might not. My suggestion that he may be is sure to get a good laugh out of the "Larsson is teh best! The difference between lottery and playoffs for the Oilers and the difference in 14 less points for the Devils!" Cult.
My point being that Larsson's future remained in doubt, less than three years ago.
I still believe we paid too much for Mueller, but I also think that we didn't. Ideally, you don't wanna give up a 2nd round pick for Mirco Mueller, of all people. With where the current market is for D-men, you're not getting someone that's very good for cheaper. David Schlemko was had for pretty cheap by Montreal this offseason, but he's already 30 years old, probably a bottom pairing guy (a very good one though) and the fact that he's quite the journeyman over the last several years, probably has also lowered his value.