The jury's entirely out on his first draft class, so I can't grade him on that. He has done a good job collecting picks, but any fool can do that (see Idzik). What's particularly disturbing about Douglas is that the players he's let go are generally doing better than expected with their new teams (Adams, Robby, Beachum, Osemele, Winters, Shell), he's gotten into scraps with Adams and Osemele, and he's repeatedly endorsed Gase even though it's obvious Gase is the worst coach in the league. Hopefully it isn't the case, but it's possible Douglas is another Gase clone who's gotten to where he is by riding on the coattails of much more successful people.
Or, you could look at it this way: the players that left and went to other teams are surrounded by better talent and coaching so they're doing better there, but they wouldn't have done the same here. And "endorsing" Gase is what every GM (and owner) does as long as the HC is employed by them - even when a HC is going to be fired you never here the GM/owner say "Yeah, our HC sucks". And who started the "scrap" between him and Adams? Wasn't it Adams who started bitching because he was supposedly shopped during last season (when it apparently was Adams who shopped himself!)? As for Osemele, he took the dispute public - I'm not saying he was wrong to complain if his injury was being mis-handled, but if you take it public you have to know that's going to cause blowback. I'm not sure why you think Douglas is the wrong guy, but I disagree.
Cutting Winters and letting Anderson walk was silly. While that's true, people forget that half the roster is out. For whatever reason that is, this team is better with healthier bodies out there. Douglas gets an incomplete right now with some questionable moves so far. Also - Van Roten is atrocious and not a starter in this league. Alex Lewis sucks as well and is widely overrated by Jets fans because he was one of two lineman last year who wasn't an absolute dumpster fire. We need two new guards AGAIN. For a team that made it's money in the 2000s with great interior line play, it's been an abomination. Pete Kendall, Faneca, Brandon Moore and even the early 2010's with Willie Colon and Slauson. It's a disgrace to have such bad guard play in the NFL.