Dany is still chasing Viserys' ghosts. It was never HER dream to reclaim the Iron Throne in her family's name. It was the dream of her half-mad brother, and abandoning that dream is the last step she needs to take in order to become her own person.
She has a far nobler cause to fight in the ONLY land she's ever been able to call home. Her destiny is much bigger than sitting on some ugly iron chair.
She will aid Westeros in their war against Winter, but she will return to her true home to rule as the Queen of a united Essos.
Bad writing would be for her to smash the slave trade, breaking hundreds of years of Essosi operations, throwing the Free Cities into chaos and war, and then peacing out to go sit the Iron Throne of a country she's never been able to call home.
THAT would be stupid.
Her choosing not to take the Iron Throne but instead head back to Essos to rule her true homeland and usher them into a united future without slavery and cruelty, then it will bring her entire story arc full circle. A queen that refused the crown of her ancestors in order to accept the one of a new world seems a very fitting end to her story.