Agreed, Guenther is the one with the big Top 10 pedigree and WJC glory, so based on that he is the one you should really be most disappointed didn't "step up" more in the Memorial Cup. Lambert already fell all the way to 30th in the Draft, so it's interesting that he's the one that remains so polarizing and that people hyper-focus in on. Frankly, given his fall, he was taken at the point in the Draft where you can hope for the upside but shrug your shoulders and realize it happens if he isn't even able to stick.
That being said, I think people hyper-sensationalize the Memorial Cup a bit too much, when it's a very small sample compared to the Best-of-7 League Playoffs.
Lambert has had a very weird season overall, but on the whole, the Seattle stint brought a very positive light for the second half of the season. Another go at it in North American Pro Hockey should have him much more confident and ready to play well.