I don’t know exactly what will make it thrive but I think it needs something added to increase longevity. More mats required/harder to obtain doesn’t really fit the bill, and extending legendary monsters health and limiting keys dropped to one doesn’t fit well for me either. It just extends the time slightly, but the end goal/reward and process is the same.
I was a big MMORPG player and those types of games seemed to have done something right to make grinding and repeating the same actions for hours on end enjoyable. Diablo 2, then Everquest, WoW, Black Desert etc. they all had me wanting for more for my character that I would just keep playing.
With Diablo 2, you were forced to live with whatever attributes you selected, there was no yellow lotus potion or respeccing. You would have to recreate your character to change your spec. A hardcore game mode like this may be interesting.
In Everquest I could camp the same placeholder for hours hoping for that named to spawn and for his rare item to drop. The lore was exquisite, you had an actual progression to raids and prerequisites you had to complete before you could even enter the zone. The goalposts were far, but with some dedication you could reach them after a few months.
I feel in Conan the goalposts (endgame) aren’t very far, you can reach them in a week or two of not even trying that hard. Then once you’re there your scratching your head thinking of what else there is to accomplish.
Maybe games overall aren’t made that way anymore, and its kind of a shame.