I could guess the exclusivity factor for those players and the only real need for the gear is raids itself.
Should their raid level gear for people who are into PvP, quest completionist or crafting?
PvP could have it's own track of gear and WoW did do this as far as I remember.
Quest completionist may not need raid level gear if they are not raiding but they could get gear with unique cosmetics and more than ample stats.
Crafters suffer from usually having better gear end game being drops. So crafting have limitations of not being an end game device. But who creates those legrndary items? Maybe there could be RNG to create legendary gear but cash shops. People also hate RNG. Needing raided items will limit this to crafters of raiding groups. Maybe a quest that allows legendary items to be created once in while.
What do you think about highest tier gear being locked behind raids? Should there be alternative paths?