I can see why Zadorov would be disappointing once you see him every game. From the highlight reels alone, he looks like a legit top 4 d-man with offence and a massive physical presence. However, he's really more of #5 that can step up into a #4 position. He somewhat frequently makes mistakes and gets caught flat footed. His offence is inconsistent.
That being said, despite these faults, he's also exactly what you want for the playoffs. His presence on the ice makes the other team wary. Sometimes his hits change the course of games. I have no idea why a team heading into the playoffs would want to flip him. Unless maybe it's part of a package to land a huge fish?