Karllson IMO is a bit over rated. I would like to di some kind a trade qith maybe our pick and a prospect for somebody that makes us go " Hell Yea!" For me that isn't Karllson.
All comes down to the contracts. I think he's a bit overrated too, but if you can get him for 3 years 9M per, I'd likely do that over a trade where they have to give up pick(s)/prospect(s) to get someone.
In that comparable, the guy you get in a trade doesn't just have to be better than Karlsson, he has to be better than Karlsson and whatever you gave up in the trade. That's going to be pretty hard to find in a trade.