This man knows his shit.
Besieging King's Landing can be equated to besiging heyday Rome.
Very little of the civilian population was killed, next to nothing in decimation, literally all infrastructure is intact AND the most prestigious and well defended keep in the country is umdamaged and yours along with the whole city.
Even fucking Brennus would jump on the chance to rule Rome.
Edit: And she fucking ruins the entire city and instantly set in motion the downfall of her reign. Nobody under the sun will trust her, fucking nobody will defend her if her dragon dies.
Her dynasty will not outlive the dragon.