Turning a 2nd rd pick + cash into a potential top 5 C in the NBA far outweighs any negatives that are on DL's record, which aren't many. Yes, in hindsight, allowing Jefferson & Millsap to walk for nothing (although using the cap space created by doing so in order to absorb salary + draft picks from GSW, during a lost season in which that cap space was useless, wasn't exactly nothing) to instead push for a playoff appearance that didn't happen was one of those, I wouldn't be surprised if that was at least partially due to KOC pulling the trump card (considering how DL handled the Kanter situation) & deciding that attempting to continue our legacy of consistently making the playoffs was more valuable than any assets we would have received in return. Moving up for Trey Burke appears to have been a significant mistake on DL's behalf (even if that decision was influenced by Corbin), but considering the team's need for a PG at that point in time & apparent lack of a leader with the alpha mentality necessary to take over late in a game (not to say that Hayward- & even Burks to some extent- hadn't shown glimpses of this), it was an understandable one.
While I can't count Hayward's contract as a complete victory (if the rumors of him being willing to sign for a Derrick Favors level contract were in fact true), matching on his contract was certainly at least a slight victory, & the $3-4 mil difference was definitely made up by the Favors contract- which was a major victory. That's not even mentioning QS, Hood, Booker, E.Millsap, & Ingles, all of which are victories of varying degrees. Drafting Exum & extending Burks are both in the yet to be determined category, while the Kanter trade, imo, should at the very least be considered a wash due to the circumstances (public request for a trade, emergence of Favors/Gobert, contract situation), if not a slight victory considering that the best (or at least better) was made of a bad situation. Not making the move sooner could be questioned, as the pairing of Favors & Kanter up front wasn't showing as much cohesion as you would have liked to see in the limited time that those 2 were on the court together, moving on from a talented young big such as Kanter that quickly is not something you do without having a backup plan (Gobert emerging the way he did & as quickly as he did really altered the direction of this rebuild). Corbin being retained as long as he was is another questionable decision, but there could have been other factors at play (such as KOC feeling a sense of loyalty towards Corbin, the FO's intentions- or lack of- to compete that last year, etc).
Considering the fact that we have no way of knowing for sure just how much of the decisions that have been made during DL's tenure (especially in the beginning) were his to make, evaluating his performance up to this point is difficult. For me, what it comes down to is:
Gobert for a 2nd rd pick & cash+Favors' contract+retaining Hayward+hiring QS >>>>>>>>>> Sap/Jeff walking+trading up for Burke+retaining Corbin
All in all, the creativity/analytical outlook of DL combined with the old school scouting outlook of KOC/Sloan appears to be shaping up into what should eventually be (if it isn't already) a top 10 FO in the NBA.