I know it's easy to reflexively complain about player development during Getz's tenure (2017-2020), but putting fact to the assertion:
2017 - Burger, Sheets, Gonzalez
Burger was developed to a starting MLB 3B. I'd call that a success. Sheets is a major leaguer, playing out of position. His hitting has regressed since his debut. Luis Gonzalez got 11 PA's with the 2021 White Sox, and Hahn tried sneaking him through waivers the next year. The Giants grabbed him up and started him for a few months. While it may not be the case that Sheets can be considered "developed", he has had success in the bigs.
2018 - Madrigal, Steele Walker, Pilkington
Madrigal was rushed by the GM, then traded for Craig Kimbrel. While Madrigal hasn't set the league on fire, he is still top 5 in bWAR for that year's first round, and has out-produced the 3 players picked in front of him. Walker was sent to Texas for Nomar Mazara, and Pilkington was sent to Cleveland for Cesar Hernandez during the 2021 pennant push. Developing players to the level that other teams want to trade for them is one method of obtaining MLB players.
2019 - Vaughn, Thompson, Dahlquist
Jury's still out on Vaughn. He was rushed, then played out of position for a couple of years. That was the GM's decision, not Getz's. Matt Thompson was brought to AA, and is considered by many, here, to be a grave loss for this organization, thanks to Getz's personal development of this player. Dahlquist has never really progressed.
2020 - Crochet, Kelly, Coffey
Garret Crochet is our opening day starter. I'm not sure what else you could say about this development success. Kelly and Coffey are both notable bullpen prospects. Coffey having looked good in the AFL, and Kelly moving up to AA.
2021 - Monty, Kath, Burke
Colson Montgomery is a top 20 in the game prospect. Having been overlooked in the draft, Monty's development is one of this organization's best success stories. Wes Kath hasn't caught on at any level. Sean Burke has pitched his way up to AAA by the end of his 2nd pro season before getting injured. He is also a success story.
2022 - Schultz, Pallette, Cannon
Noah Schultz is a consensus top 100 prospect who is being brought along slowly. Pallette came back from injury, and Cannon will most probably pitch at AAA in his 3rd pro season.
Out of these 6 drafts that cover the entirety of Getz's time as director of player development, I would say only 2 of the 18 have been development failures. The others you might cite as not hitting their ceilings with the Sox were either traded, or rushed by the previous regime. Burger, Madrigal, Vaughn and Crochet are contributing major leaguers. Thompson, Kelly, Coffey, Montgomery, Burke, Schultz, Pallette and Cannon are well-regarded prospects.