For me, it’s probably unfixable, because all the problems the show now has has stem from two decisions D&D made long ago:

Cutting Young Griff from the story (who is supposedly Aegon Targaryen, Dany’s other ~~brother~~ nephew, but who might have been fed lies about this by Varys). Who, in the books, will likely be the one to take King’s Landing from Cersei after her Sept of Baelor stunt and be welcomed by the people. He already has the backing of most of the southern Kingdoms (that have been forgotten by the show), which makes Dorne relevant and gives the Tyrells someone to rally behind, too. Thus, when Dany arrives expecting to be welcomed with open arms, she’s shunned as an invader and usurper by the people while someone who theoretically has a better claim to the throne than her sits on it, making her turn to cruelty make more sense.
Stripping almost all magic from the show. The Starks are all supposed to be wargs (Bran should have been doing some warg-fighting in episode 3), Jon’s resurrection should have had more consequences (foreshadowed by book Beric and Lady Stoneheart), and the big one - Euron Greyjoy is supposed to be a goddamn pirate wizard who used blood magic and has a horn that can bind dragons. Book Euron is way more interesting and will probably be the one to steal Dany’s dragon and bring down the Wall, eliminating all that bullshit from last season.

There are more nitty-gritty issues than this, but these two major things caused ripple effects through all the other characters - Tyrion is now a moron, Varys and Littlefinger ended up purposeless because their endgame plans relied on characters that no longer exist on the show, Dany seemed to decide to burn innocent people for no reason when it should have been anger at them supporting Griff instead of her, Bran just sits there being cryptic, Cersei stood on a balcony for at least a season after she should have been dead already…

I could go on but I’m burnt out.

Basically, I think some editing might be able to salvage what’s there to some degree, but the core problems started with decisions made years ago because the things that were eliminated weren’t massively important yet as of book 5 with little thought as to how they might affect the ending. Now that we see what the bones of the ending are, we can see what purpose those seemingly out-of-nowhere book 4/5 things actually are meant to serve.