I don't really disagree on anything you said here. There's a lot of bad mentioned here, and many more unmentioned. But how to square that up with the good moves they've made? Well, end result is that they still put together a very good team because their positive moves were good enough to get them here.
Overall, they've had good run. I'm more skeptical of that going forward. If I was to grade how they've done, I'd say a B+ or even A- is fair. Putting together a 50ish win team off the backs of draft steals (after trade ups) and UDFA is really difficult to do. I just don't think we give them enough credit for nailing the moves they did. In some ways it's a testament to how good the Gobert+Mitchell moves were that you can still make plenty of awful decisions and still come away with a good team year after year.
If I was to speak on my confidence going forward, I'd probably agree that C+/B- is more fair. This last and most difficult step of becoming a true contender is proving to become difficult and they've squandered two really good opportunities to do so. The initial Hayward deal is easily the worst and most unforgivable mistake IMO. It may also be the reason why we can't renegotiate a deal at anything less than a premium.
Those moves are the ones that really matter. Penny pinching Hayward so he's able to become a FA a year early was devastating. Trading the farm for Mike Conley was devastating. Ed Davis, Tony Bradley, Rayjon Tucker....yeah those moves are really bad...but in reality they really should be afterthoughts compared to these other pivotal moments. I understand if they lower your confidence going forward (sure does for me).