I understand your viewpoint about Karlsson's value, and I would not disagree. But at the price you are suggesting, which may very well be fair and in line with market value, I think it is extremely unlikely if not entirely improbable that Colorado is involved in those trade talks.
If Karlsson makes Colorado an immediate cup contender after making that trade, maybe Colorado does it. Do you feel like Colorado would be one of the top cup contenders if that made that trade? Ultimately, my point is that I don't believe that it does make Colorado a favorite, which makes the cost too much under the circumstances.
I think Colorado's defense would look a lot better with Karlsson on it than with Makar or Girard, that is for sure. He is 28 y old, it is not like he is old or anything, and I would think he would certainly consider signing with an up and coming team like Colorado, especially if they treat him and his family well and they make the playoffs (i definitely think they will this year with him in the line-up). It is not a complete "win-now" move, that is for sure... I don't remember the last time a 28 y old generational defenseman was for trade, and I'm pretty sure that if you don't get him now, you probably never have another chance in getting him later (even if he goes to UFA then you will compete against 29 teams (he woukd not go back to Ottawa)).
I don't see why it would prevent them signing Barrie. Rantanen will see a raise next year and I expect them to resign Varlamov, but they have a lot of room, and it should stay that way a while, especially if they trade Kerfoot + Girard.
Who is going to maje that much more money in the near future?