I really only have 2 complaints and if they had done the forst, the 2nd never would have come about. I'll start with the 2nd, which is simply they should have done whatever qas needed to land Giannis. Give him whatever salary he wanted and throw in the extra draft pick or young player. They needed to get it done
The 1st and biggest criticism is simply Brad waiting a year to do this. They should have just thrown in the towel last summer and traded Brown and White, not made the Mann dump off and collected a boatload of picks, young players, etc. all while tanking last year to land a high pick in the last draft. It was obvious to me that that was the best strategy. I think analytically they felt the team was going to be bad last year so they didn't need to go full bore, but they were wrong. The team still somehow won even with it still being better with Brown on the bench.
I obviously am not a fan of the Sixers trade, but if they made that trade it was because it was the best offer and the offers would only get worse. And they needed to move Brown, so it is what it is. They just waited a year too long and then bundled the Giannis trade. Those are the real errors.