Everything took longer, thus feeling more rewarding when you finally finished.
the 'newbie' feel.
Class quests at 60.
Some quality off life improvements would suck to not have, but for the most part I would be fine.
One reason for WoW decline I often hear is that its an old game and naturally people get bored with it. But TV is much older and people still watch that. Surely if a thing you once enjoyed keept staying fun, you would still use it?