Eh, Duran is a solid prospect but he's not a Berrios level prospect, let alone a top of the rotation type. (Although, as you say, baseball may be moving away from that). If you don't think a nucleus of Buxton, Sano, Berrios, Kepler, Rosario, Garver, Polanco etc was a nice situation to build around, I don't know what to tell you. It seemed like a pretty good place to be. Certainly a lot better than our current situation. That nucleus was going to be pretty good, no matter who was running things, and they were. But I think a better FO might have been able to help the players more (although the Cruz signing was good). I also don't think this is there only one bad offseason. They've had several bad offseasons where they haven't significantly improved the team.
There are good things that Levine has done - I liked the Donaldson signing, a lot, even though it hasn't been as good as we all hoped. The 2018 draft looks solid. But he seems to have misjudged the talent in the system several times. He was not able to keep the window of opportunity for the above named nucleus open.