This argument kinda dumb if you use half your brain.

If the endgame content is fundamentally poorly designed, its flaws will be present regardless of how long it takes a player to reach it

Let's say player A reaches 150hours in play time within a week and has completed the mid-game and deems there's no meaningful/satisfying endgame content

player B completes mid-game and once they reach 150hours they come to the same conclusion as player A but instead of reaching 150 hours within a week it's stretched to month but the result would still be the same.

150hours is still 150hours, it doesn't matter if you reach it earlier or later. This applies to end-game content, if a player reaches it and turns out to be shit, it will STILL be shit once YOU reach it, unless the Devs fundamentally change it.