Any cup contender doesn't "need" a 1st (better way to word this is that a 1st becomes much more expendable). The Blues in my opinion would qualify as a cup contender. It's definitely true that Buch gets carried thanks to playing on a line with Kreider and Zibanejad, but middle 6 forward isn't what Buchnevich is. That would only be his role if he were playing in St. Louis or another comparable team. Skjei is a LD by the way, while you're right comparing values of two different positions is a separate case, he wasn't really THAT much of a market commodity.

In other words, Buchnevich definitely doesn't satisfy the conditions you're looking for to part with a first, but he can definitely net that return whether it's from St. Louis or someone else.