Initially reading this thread I was concerned about using the alt method to reset my team at the start of the instance without leaving the instance.

After getting more details and understanding people were repeatedly farming bosses over and over without clearing to them I agree that is definitely an exploit.

I don't know if the alt resetting my instance while my team is logged out is even using another layer. Usually they come into the same layer as my other team members so I wouldn't think so. Regardless I don't think that the alt reset approach is exploiting (I have to clear the whole dungeon again) and unless/until I hear otherwise I plan to continue using it.