NSH should've tried to get at least a 5th rounder minimum and tried to sign Galchenyuk in FA
That is a bit of a nit pick to say they should have gotten a 5th rounder. That is negligible value wise and doesn't change the concept of the deal.
Johansen did not have trade protection. They traded him within the same division with the max salary retention for nothing. That is a pretty damning indication that they had zero leverage. People in this thread are years behind on the player. They didn't trade the Johansen of 5 years ago. Colorado took all the risk in this deal.
Here is how you logically evaluate the deal.
If you are Nashville, and Johansen's contract was expiring this off season, would you retain him on a 2 year extension with a 4M AAV? Probably not. Therefore, trading him was the right move.
If your are Colorado, and Johansen was a UFA, would you sign him to a 2 year contract with a 4M AAV?
He is a flawed player at this point, but Colorado may have looked at the UFA market and determined that it was a risk worth taking. There is also the reasonable possibility that this is a win/win deal. Colorado didn't have the same baggage that Nashville does with the player. In Nashville, he was positioned as a core guy and likely a primary leader. In Colorado, he comes into an established room and team structure as a complementary player on a team that already has their leadership core sorted out ahead of him.
There were a bunch of hot quotes about Phil Kessel winning all these cups, despite accusations that he was a poor leader, but there is a difference between being positioned as the star of a team who is expected to be a primary leader, and coming into a team like Pittsburgh that already has those guys, or even going to a team like Vegas as a complimentary veteran who isn't going to play every night. I have no idea if Phil Kessel was bad in Toronto or whatever, but the point is that if he was a cancer in Toronto as a primary leader, winning the cup as a depth veteran in Vegas doesn't invalidate that.
Nashville wins the trade because they get something tangible and defined without risk. That is, 4M x 2 years in cap space. This could be an Adin Hill type trade where we look back and a player vastly outperformed what was expected when they were acquired, but odds are Colorado either regrets this deal, or it ends up being mostly irrelevant with Johansen living up to his deal but not exceeding it by much.