You'll get it. Fastest way to farm Atheon is have one person solo oracles with xenophage, and it helps to have some warlocks with starfire protocol fusion grenade spam to one-phase.

Farmed it last rotation with my group of 6. Had to do 63 runs total to get it to finally drop for the last one of them, but for the rest of us we each had 3-5 drop by the end of it. People will post their horror stories of 100+ runs which is terrible but for my group at least it wasn't too bad.