Yeah, but GRRM wants his Scouring of the Shire. And he said that theme of his story is "human heart in conflict with itself". That has to play a role in the climax of the story, WW are just enemies, there is no internal conflict there.
But that's what you get with Daenerys, Jon and Tyrion at the end of story if you remove WW earlier. Constant internal conflict. Love and duty. Family, honor, power, all these great themes that made this story great and that GRRM loves so much.
And also the message is that humans are the biggest monsters, not some ice demons. Removing WW earlier and making the final conflict between Daenerys and everyone else makes the story much deeper thematically. Otherwise what is the theme of the story? We should unite and save the world? "Avengers assemble"? Where is human heart in conflict with itself there?