(that challenge is a remnant of the past)
Challenge isn't a remenant of the past. Challenge due to game design defects is. Everquest and FFXI weren't successful because of punishing death penalties or hours of walking. They were successful because the battles were fun and the experience was immersive. MMOs fail because they get half-assed in a genre where there are already too many to choose from. MMOs don't succeed or fail purely because they are or are not challenging enough. They succeed or fail because of poorly designed mechanics, clunky user interfaces, copypasted NPCs terrain etc, and general half-assery. MMOs are huge projects. No matter how huge your game world is, the players expect you to fill it and keep it interesting. But the bigger it gets, the harder it is to accomplish.

FFXIV tanked at launch because they half-assed it. Then SE learned their lesson and began to take their time to make more of the right calls.