There is a good ending to Game of Thrones: evil wins, everyone dies. All the fools who pursued their own interests rather than face an annihilating threat get annihilated. It's right there in the show's motto. "Winter is coming."

The writers just lacked the courage to do it. They tried to tack a Disney ending onto a tragedy.

Either that or Cersei being queen would've been the correct ending.

The Lannisters would've had the only real army left without that WWE-style defeat of the Night King. Cersei's consistently outwitted everyone (except Tommen, I guess), and they knew how to buy loyalty.

Instead we ended up with the usual plot armor, and a "twist" that the character that behaved like a tyrannical zealot for 7+ seasons was, in fact, a tyrannical zealot.