Hard to understate the incompetence and ego at play here. Trading Luka for AD destroyed this organization, fanbase, and team for all of the reasons mentioned since that day. But holding onto AD at this point is just doubling down on your embarrassing mistake. The "problem" for Dumont is that if he does the smart thing (fire Nico, fire Kidd, trade AD) he is admitting his mistake within the same calendar year. That is too much of an embarrassing thing to do and his ego won't allow it. So instead we have to watch the Mavs pretend and talk like they are contenders, when in fact this roster makes no sense, can't shoot, and is mostly washed and injured.
In the meantime they inexplicably were gifted Flagg who may end up being great, but still too early to say for sure. They now have an impossibly small window now to build around Flagg by tanking hard again this year and pairing up a top prospect with him. The obvious things to do are to trade AD for some minimal value, buyout Klay, and frankly I would be open to trading anyone on the roster not named Flagg for future value, even Lively who I don't trust to stay healthy, and Kyrie. You have to do everything you can to be bottom 5 this year, last chance.
I'm guessing there are still AD trades to be made, but it won't bring much back in assets. Probably need to find a team with top 10 title odds with a few mid to bad contracts and a 1st round pick to give back. Either way, get this guy out of Dallas and get a GM with some kind of vision for how to fix this mess.