It's not so much about nerfing content but more about offering a new end game challenge build around testing players' ability to play their jobs well as opposed to dodging one shot kill mechanisms.

It could be about content that need tanks to know how to put up the best hate best damage mitigation while generating high snap aggro.

It could be about content that need healers to clear debuffs fast. Or DPS using their utility skills to disrupt enemy moves or debuff the boss.

It could be a randomised dungeon crawl filled with deadly enemies...

Just do away with the irrecoverable one hit kill.