The initial Wuhan outbreak is completely inadequate for estimating the mortality of an unchecked wave. It was weathered with massive outside help, being surrounded by the most powerful and agile economy in the world and all that. The rest of the planet is hit concurrently, there are no unaffected regions left who could send help. And that local wave was successfully interrupted long before reaching anything close to herd immunity, so peak medical demand was still far below worst case.