Donovan and deHaan have been successful EVERYWHERE. That's clue #1, not because they are "an Islanders prospect"
Not every prospect reaches their maximum upside, almost NONE of them reach that (or anywhere close) in their rookie year. Add a terrible team, terrible coach, cheap owner, sprinkle a few key injuries and it's not exactly an environment where many can succeed.
If you want to take a snap-shot of Donovan as an Islander, in the midst of this losing streak, in a bad season, and write him off, then fine. To suggest he's not a good prospect is just naive.
The NHL is FULL of young defensemen who struggle. Heck, it's full of old defensemen that struggle.
Who exactly do you suppose would be better? Look around the league, all teams need defensemen and there are very few great ones, a lot of bad ones.
I'm not suggesting Donovan or deHaan will be all-star NHL dmen. They are very taleneted, have had success at all levels of hockey before the NHL, they have potential.
If you've seen enough of Donovan to classify him as a bum, wonderful. I'm sure there are plenty of teams that will grab him once he's waived. Maybe he's the next Gervais or Campoli or Hillen. Maybe not.
Isles are a team relying solely on drafted players to carry the team through this "rebuild" - if you believe that, then you have to understand young players, especially young defensemen, need TIME and SOME will get better, some won't.
I happen to think BOTH Donovan and deHaan will have long NHL careers.
What I see in Donovan is a smart offensive player, good instincts, good shot, sometimes makes poor decisions with the puck and struggles with positioning at the NHL level. There's not a young defender in the NHL that isn't in exactly the same boat. Carlyle says the exact same things about Morgan Rielly and Jake Gardiner. Cam Fowler was awful defensively as a rookie. Michael Del Zotto still is.