I mean, I'd get it if Willander were a franchise-level D prospect. But he is not at that level. If you were shopping him for a draft pick, I doubt someone would give you, say, a 5th overall for him. Yet I bet a number of teams would gladly offer up a 5oa for a legit young NHL scorer ... but the team with that playe probably wouldn't take it.
Reverse the situation, if I had a young impact dman, vs. a good but not considered franchise level forward prospect, would I trade the latter for the former? In a heartbeat. The proven impact player is more valuable than the vast majority of prospects. Take a typical mid 1st round pick, and you're far more likely to be able to replace a Willander level prospect than you are to be able to flip that into a mid 20's impact player at any position.