I think perhaps the most reasonable argument I heard regarding this was from "
Hello Future Me" (key part coming in around 23:30) that while "Mad Queen" Daenerys would likely work as a culmination of the arc for Daenerys as she appears in the books - which have put in the legwork to justify it - it doesn't really work for the Daenerys of the show. The show simply did not sufficiently set that up for this to be a satisfying conclusion for her. That it is instead better for her to come to the brink of that decision, where torching the Red Keep would secure victory, and in that final temptation, refusing that route, and losing because of that decision. I think he phrased it pretty succinctly, so I'm just going to quote him directly here.
The overarching theme of Daenerys's story is that the moral leader is not necessarily the best one...though Dany may have freed the slaves and defended the weak, virtually every city she has ever ruled - especially in the books - has ended up worse off than before her supposed liberation, through corruption, insurgency, starvation, and disease. The greatest challenge of her story is that she has found that being a good leader means compromising her moral character. And faced with this ultimate test, it's more consistent with her character in the show, and more meaningful to her arc for her to end in keeping her morality by giving up the throne and proving she is not her father, as people feared.
This also gives more meaning to her vision from Season Two. She doesn't just never reach the Iron Throne, she chooses to turn away from it.
I'd go further and say that the Mad Queen angle fell flat because of how they'd set her up to be a foil to Cersei. We see their similarity in their ambition and willingness to play "the game", but there's a profound contrast in everything from their relationships with their brothers to how they treat their subjects. Whereas Cersei antagonizes her subjects and sees them as tools for her political ambition, Daenerys let her empathy for her subjects guide her in a way that frequently blew up in her face. And that's something that was carried all the way to Season 8. Whereas Daenerys shelved her ambitions to fully commit to the war against the Others and protect life, Cersei withheld the promised aid to that same fight, risking the lives of
literally everyone in a gamble she thought would let her secure the throne for herself.
The icing on the cake, of course, is that this recurring contrast between them basically spells out why Daenerys torching King's Landing should have been off the table.
Cersei already did that, and while there's enormous power in a foil refusing to cross that same line, having them suddenly break their contrast for "Round 2" of the same - but greater - atrocity does not make for a satisfying final act.
www.escapistmagazine.com
