True, in worst cases buster dots do not calculate the Invulns damage taken, P6S will shove around a 26k dot soloing the shared, around there for P7S.
Can easily manipulate it in P6S. Invuln the 1st, take it back once bleed dropped off, tank swap as normal. The 3rd buster or further will be a shared. 1st is guaranteed to be Shared, 2nd always spread.