Forgive me if i am missing something here, but would it not be best to have the boss non-instanced like it currently is, as well as an option to make the fight instanced? That way both groups and solo players can fight the boss as much as they like.
It's really hard to balance a drop-table for both instanced and non-instanced versions. I also feel like making it an instance is not required after seeing how much it has quietened down since the initial release.
If it was instanced the cudgel would probably have been at least 2x the current drop-rate if not more in order to compensate for the number coming into the game.