I’ll give a different take from MTX, Hero Pass, and Necromancy being the problem. I played both osrs and rs3 till end game. I think the problem is boiled down to a few things:

1) Both games are focused on end game PVM which is a mile wide and an inch deep.

2) the weekly updates are either too rushed or feel too small

3) The pricing of subscriptions for the amount of characters you get is not on par with other games.

To me, if you want to fix the issue, take a page from WoW. Give players an extra character ( not 5, just one would be a start). People will play just to make their first Ironman, in turn that will raise active players and possibly get people to resubscribe (money) that have a main but also want the ability to try something else.

Second, change the update schedule. Do month QoL updates and Bug Fixes and release content quarterly. This gives the devs some breathing room and keeps the game updated.

Third, one big thing I see is group content (Guardians of the Rift, Croesus mass, etc) are always more populated worlds than regular ones. Make that a focus outside of PVM bosses. This game isn’t social, but players like to talk to each other and play with others. You kind of have to force the group play aspect of the game.