I think the screw up with Queta was Brown didn't want to invest in a development project when he was trying to win now. You could say the same about Sasha, you could even say it with Davion, Keon. For some reason he had a much wider leash with Colby.
The fact that he wound up on the Celtics was more to do with their cap circumstance and lack of options more than they picked out a gem in the rough. They signed him to a 2-way and then had no options but to bring him up because they didn't have big depth when Tingus Pingus was out so much and eventually converted him. In the process he got the minutes needed to develop into a serviceable NBA backup big.
Sucks because he was ours and I thought it was a great pick at the time. I hate to dogpile on a coach I genuinely liked and who helped us break our playoff drought but beyond the lack of defense when that was what we were sold, the failure to develop young guys (to the extent where even fans were turning on Keegan) is unforgivable when you are not only trying to win now but develop sustained success. The end of the golden years was largely a result of letting a few young pieces get away while whiffing on a few other picks. The Wallace situation also completely sucked and was bad planning on our end. But shy of doing an OKC and selling off your team while they are still playoff level that's what teams have to do to maintain, always have a next man up. I think Monte has shown skill at finding players late or UDFA but you still have to make them NBA players and Brown didn't seem to take that part of the job as seriously.