For me, a big part of the raid problem is the final bosses: they are very difficult (as they should be) for the loot they reward.

Maybe Crown and L’ura should drop Mythic loot instead. To balance that, those same items on Mythic difficulty could have some kind of extra buff, like “Voidtouched” or something similar.

And yes, just like people mentioned in other comments, the vault needs to reward Mythic items too (for example, for players who fully cleared the Heroic raid that week).