Karlsson had just won the freaking Norris trophy and they got him without giving up a ton.
It was a worthwhile risk to take, their core group is just too old and Karlsson I think has a weird thing about not being the absolute alpha on the back end (seemed like in San Jose he only really took off once Burns left).
Karlsson is definitely not an easy player to work with, but if you do decide to work with him, you should accomodate him. He's not doing you any good if you make him be a 50 point generic #2 defenseman. He's not good at that. He needs a free reign and complete freedom. Can't give it to him? Don't trade for him!
If Dubas was going to trade for Karlsson, he needed to clarify this with Sullivan, or fire Sullivan. Karlsson can be very effective, but ONLY if you let him do what he wants, and deal with the repercussions. Otherwise, he's not worth it. He's not going to reinvent himself at his age.
Karlsson is the ultimate "orchid" type player. Either he's amazing, or he's absolutely awful. He requires the right environment.