We are both around the same level doing corruption 300, and above CoF 9. I was joining the boss runs (so I was not host).
Basically it seems that I only got loot that dropped as if the boss was a normal monster (though it did drop it’s loot table items). We did around 12 or so runs, and out of all of them the boss dropped 4 uniques and the rest being rare/magic. Some were done with harbinger, and we even switched monoliths. I even relogged and rejoined the party. This is abnormally bad loot rolls.
As if monolith farming in a party wasn’t anti-multiplayer enough without game breaking bugs.