The mess Middleton created.
Ironically Klentak's biggest trade/free agent moves once the rebuild ended were almost uniformly good, in and of themselves: Segura (even if we didn't like the price), JT and Didi (the first time) Wheeler. Only Cutch a big disappointment but he wasn't a total washout.
Relievers, of course, not so much. And that has basically continued. And drafting and development the real problem. Klentak certainly didn't create that problem, but it was the one problem (along with analytics) he was supposed to fix!
At least neither of them have signed any failed expensive starting pitchers (Arrieta was a disappointment but not a failure).