Simple solution.

Make an extra mode. An "Savage-practice" mode for lack of better term.
This mode should be the exact same as the savage varient EXCEPT for the fact the machanics are FAR more forgiving. insta kills reducing your health to 50%

This mode should hand NO LOOT at the end (since you have not yet earned it)
But if you complete the battle correctly, you get a special achievement. The you can make create a party finder with a new mode "Duty-practice complete". Here you can look for other players whom have all practiced, done the work, know the mechanics but don't yet have the kill

I believe this mode would be a crucial middle step. as right now casual players that want to experience the savage content AND progress are completely lost. Not everyone has time to commit to a static group. people have full-time jobs. Some of us have multiple full-time jobs!! That should not forbid us from experience the ultimate encounters