I think you answered your own question there with a lot of reasons why his reign as managing partner has failed, year after year. And he didn't need to convince the "ownership" to go above the luxury tax, he's already 49% of that decision and only has to get one other entity on board. The Bucks seem to defer to him on everything, I doubt they had even a seconds worth of input on MacPhail - Middleton was the one who needed the security blanket, and deferred to Gillick too.
Now is nothing like when Giles and Monty had their meager % and had to answer to four or five people all of whom were also old. The ironic thing is this is a younger generation - it is not Middleton's father, or the Bucks' parents. But they still seem old (or old-school).
I mean, he's the owner, he's not going anywhere. But he's also not a new owner. It's great that he's rich, but he's shown no facility for hiring good people, actually changing team culture or making a single good decision, going back to the Howard extension (which he was obviously the key person who had to sign off on that with Monty) and the Burnett deal (which also delayed the rebuild). And since then, all the hands-on moves he's made. Not all of them terrible, he just shouldn't be the one making them, and up to this point, he has not hired any good people. The Girardi era is likely almost over and there's already only two years left of the Dombrowski era (at least for now). If he does leave hopefully he'll have left behind a franchise that is in better shape, but there probably isn't gonna be a ring, and that's the standard Middleton has claimed to have, since 2009 as well as 2019. I'm also not going to applaud him for passing the CBT this year when it should have happened each of the last two years.
I think you are probably right that Dombrowski is the best-case scenario in terms of being a Roseman type for Middleton. And Fuld, and the recent hires, seem much better than the Klentak front office. Perhaps when Fuld is President and Kilambi is GM it will be a new dawn. Led by mostly Klentak draft picks (Bohm, Stott, Abel, Moniak?) if we're lucky.