Overall I agree with the majority of your take here. However, the two real issues in Dallas that (probably) won't be solved by just hiring a new GM and head coach:
1 - Does Mark Cuban empower the people he hires to do particular jobs? There have been rumblings for years that he really makes a lot of basketball decisions and/or will listen to different people at different times. For example: someone other than the GM, like a highly opinionated, former professional gambler. It's his prerogative to do whatever he wants, but without some semblance of a chain of command there will be constant power struggles and, at times, poor morale.
Same with the head coach. If players feel his strings are simply being pulled by others, the respect won't be there and they won't respond to him, no matter how sound the schemes or motivational the words.
2 - Will Luka Doncic mature into the leader the Mavs need to build a championship winner? The guy is a superstar, the exact type of player an organization hopes to land with a high pick. However, he's a bit volatile (just young and competitive?) right now and that will need to eventually change. You can't be outwardly yelling at your head coach every time he calls a timeout you don't agree with (or the officials on every call). That behavior is understood occasionally, but reading reports it sounds like he needs to mature a bit.
As importantly, his heliocentric game is great right now. Doncic has proven himself, puts up crazy numbers, and looks to be a force for a long time. The team won't be championship caliber until he's willing to play off ball at times as the talent around him improves. He'll need multiple players to be more than just shooters to win a title and for that to happen his game will need to continue to mature...just like his leadership.