Im hardly disagree with you on dat point.
For a long life on an MMO u have to have one of those 2 things to keep the playerbase with things to do.
1- Pve focus aspect: U need those hard mechanic, epic batlles, big groups raids as we all known in wow, or some kind of infinite progress system for instances.
2- Pvp focus aspect: U need any competitive area where people can reach a ladder and get into get better. Dat even gives you visibility on stream platforms and stuff if its balanced and engaging.
3- ideal world, both of them. But do u see the patterns? Repetitive engaging and infinite content for game longetivy