Walman has negative value. The only halfway reputable source to report on this has been Frank Seravalli who said GMs were surprised at how significant the sweetener Detroit had to attach was, not that they were surprised a sweetener had to be attached in general.
So instead of calling up every team not on Walman's NTC to maybe offload his contract with a 3rd or 4th instead, Yzerman attached a 2nd and got it done immediately. The difference in value between those picks is ultimately insignificant.