1 - Is it under valuing Knight or is it realizing that goalies are the most difficult players to identify success.
In 2012 there was 24 goalies drafted, Vasilevskiy was the first drafted 19th overall, Hellebuyck was the 13th goalie taken at 130. Saros was the 9th goalie taken in his draft year 99th overall, other than Jarry, the 44th pick in the same draft, none of the other goalies taken ahead of Saros have ever become NHL starters. So while Knight is a good prospect and has shown some success in limited NHL games, it is not unreasonable to think that a comparable goalie can be found in the 3rd, 4th, 5th round. To use your teams best trade asset (Arizona - Chychrun) and have the "best" piece in the deal be a prospect goalie is underwhelming and has the potential to be a terrible deal for the Yotes.
2 - Denisenko, I'm not sure why he should be valued as a key piece in a trade of a player like Chychrun? He is in his D+4 season. He hasn't really produced offensively the way you would want in the A or the KHL. I understand he is still young and has room to improve, but a key piece in exchange for a high end #2 dman needs to show more if the value is going to make sense for the team acquiring.