There is so much turnover in the scouting/development department (the Brewers were literally among the worst in all of MLB before they started overhauling things once Mark A bought the team and that process continued further once Stearns & company got here) that I'm not sure how big of a developmental indictment some of these guys actually are.
Another thing to consider is that developing catchers is literally the hardest thing to do, so every team's top prospect lists are likely similar rife with "failures".
The most informative thing I think with regards to future expectations would be that despite whatever developmental shortcoming they may have had, since Stearns and company have gotten here Brewers catchers rank 3rd in WAR among all MLB clubs.
Outside of the one year of Yaz, most of that WAR came from players that came up through the system (Lucroy/Maldonado) or were targeted by Stearns & company in trade (Pina/Narvaez).
Between Contreras on the MLB side and Quero in the pipeline, I think the catching situation is probably the best its been organizationally since Lucroy/Maldonado were coming up.