Being a mediocre GM doesn't mean he's doing crazy shit like proactively acquiring a 2nd round pick then offering it to only one team as a sweetener for taking Walman.
Yzerman has signed plenty of bad contracts and Walman is certainly one of them. Soft third pairing offensemen are not a valued commodity. Good on Grier for taking advantage of the situation but this trade is perfectly reasonable on its face. No need to speculate about some side deal.
I think the truth is somewhere in the middle here.
Walman is not a bottom-pairing offensive D, he's actually more like a middle-pairing offensive D who was in over his head on the top pair but sort of held on with Seider. He's not a nobody, he's not a major somebody either, and he's not terrible. But at his current cap hit, most teams wouldn't want to make a spot for him.
The teams that have cap space and would consider this move is a shorter list, and the teams that have cap space AND see him as worthy of a roster spot for less than a 2nd round sweetener is shorter still.
The Sharks, of course, are so bad on D that he immediately becomes arguably our best D and may play with Ferraro to help us get out of the F'ing defensive zone every once in a while. Very few other teams could say this. Couple this with Yzerman apparently being desperate to open up cap space either to sign Gostisbehere and/or a big FA fish, and you have what appears on face value to be an excellent move by Grier.
It does seem karmically in balance with the Goodrow situation. But taking all four moves - the Wiesblatt trade, the Dellandrea trade, this trade, and the Goodrow pickup, I think we've added pretty well to the bottom/middle of the lineup in the last week.
We still need another "top pairing" D and at least a top 6 C/W. And even then... gonna be a gross year.