I would do 3 things

Rework the ilvl sync so that it constantly gives challenge and that you can also use later movesets at reduced potency
Rework crafting and gathering and make them much more involved like bringing expert style recipes into the base and making expert even more challenging...really reward those that go for it and make it less macro dependent...this also stems in the levelling of those jobs being much slower because now they are a joke.
Introduce Bozja style critical engagements to the open world...have them per expansion and have them even offer Bicolors or another currency and make the items rewarded grindy in a sense it would take doing a fair few to unlock 1 thing for instance...this would allow for people to engage with the world zones much more.