I agree. I mean, for the sake of argument, let's assume we're only trying to fix S8, and that everything before S8 is set in stone.
Let's also assume we know that the storyline has to hit certain immutable beats (most or all of which I assume came from GRRM): the final battle with the AOTD is at Winterfell, Dany burns down all of KL, Jaime and Cersei die together in KL, Jon kills Dany, Bran becomes king, Sansa becomes QITN, Jon is exiled to the NW, Arya leaves Westeros forever, and Tyrion becomes Bran's Hand.
Finally, let's assume that we only have the same amount of time (give or take 440 minutes, or approximately 7.5 hours) worth of episodes to hit those beats.
...Personally, given those constraints, I don't know how much could really be fixed. You still only have six episodes to take Dany from madly in love with Jon to being killed by him. You still have Bran's robotic TV characterization to deal with. You still have Jon's parentage amounting to nothing in the end except a source of conflict between Jon and Dany. There are some changes I think would improve things:
1. Making Bran seem less detached and more kingly, and showing other characters pick up on this. Have Tyrion/Bran have a conversation about power and what's best for Westeros (of the type he had with Varys).
2. Having Jon volunteer to go to the NW to protect Bran's crown and to ensure that no one can use his own claim against Bran.
3. Eliminating the Bronn assassination subplot.
4. Making more space in 8x06 for proper epilogue stuff (Sansa releasing Brienne from her service, e.g.) by cutting the long scenes of Jon and Tyrion walking through the city.
5. Leaning into the idea that Tyrion's love for Dany was blinding him to her true nature, instead of Tyrion randomly announcing in 8x06 to Jon that he was in love with her, too. I mean, heck, Varys could have thrown this in his face in 8x04 when they were arguing over Dany.
6. Giving Arya's NK kill to Jon. It did nothing for Arya's arc and it would have gone some ways to fuel Dany's jealousy of Jon.
7. Include in-text explanations for some of the dumber decisions the characters make, like a line of dialogue where the characters dismiss the danger in the crypts because they don't think the NK will use his resurrection powers, or a line of dialogue that shows that Jon's dragonriding was at the very least raising eyebrows about his parentage, or a line of dialogue at the war council where the possibility of Arya assassinating Cersei is discussed.
8. Eliminating the Gendry/Arya sex scene, Gendry legitimization, and his wedding proposal. The same thing could be achieved by Gendry reaching out to Arya and trying to make plans with her, only to get gently shot down with "That's not me."
9. Showing the cracks in Dany's confident, genial facade in 8x01 and 8x02 more clearly, like a hint of genuine menace or danger in 8x02 with Sansa or having more of a rage meltdown with Tyrion.
...Still, most of this is purely cosmetic.
I'm not sure that the elective monarchy idea is from GRRM. I actually prefer the idea of Bran and Tyrion just taking over in the power vacuum after Dany's death. You can still have the council scene, but instead of the lords and ladies electing Bran because he has the best story, it would be Bran and Tyrion announcing that Bran's going to be king, the North is seceding, no one else gets to secede, and everyone's going to have to just shut the fuck up and get over it.