This is my read on it too, and ultimately the show and story feels really nihilistic.
My question is actually how long Bran's rule lasts. I think it's less than 10 years.
1. Bran is an incredibly weak king. He has almost no claim to the throne (by Westerosi standards), he is unable to sire children, and apparently he's going to be a puppet ruler where Tyrion controls things, who is an unpopular guy with almost no power base since the entire Lannister army is decimated. Also, Jon didn't denounce his claim, he was punished, giving anybody wanting to challenge Bran's claim all kinds of ammo.
2. Dorne is probably EASILY the stronger power left in Westeros. I can't see them sitting there like you said.
3. Yara had a promise of independence. The Iron Born are not going to sit on that. Plus, there is absolutely nothing to stop them from reaving from the wall to Dorne.
4. For all we know the Dothraki are still there. That's going to go well. Probably the largest and most fearsome standing army in the country by a mile.
5. The Starks just basically rule everything? That's going to rub a lot of people the wrong way.
6. The Iron Bank is still owed a TON of money from the crown for the hiring of the golden company. The tax base of Westeros is basically destroyed... how is Bran going to pay that back...with Bronn as your master of coin?
7. Bronn is basically the ruler of a depopulated area? So the Lannisters just killed everybody in the Reach apparently.
I mean it's hard to imagine just how destroyed Westeros is right now outside of Dorne and maybe the Vale, however I have to assume most of the knights of the Vale were killed in the battle of Winterfell.