Anyone serious is on a weekly schedule with a regular group. By this point, I find it difficult to believe that that group has much more to gain from bosses that they've been farming for what is now, several months. If you have, then you either started late or had a lot of turnover in the group - at that point the collective seriousness becomes questionable.
I think the susceptibility to disconnecting players on phase changes is probably a good start for that argument; and not really sure it need go further. Encounters need to be, first and foremost, stable.