If they made the stacking potency only activate when exposed it would fix the loop without messing with any other team. 1-5% bonus tenacity (stacking) each time traya is exposed, resets when someone stands alone.
If they make it 1% this team would still be viable but would definately need a high gear team to drop decent damage before her tenacity stacks enough to resist exposes. With a high gear team it might be possible to stand alone and kill sabers again to get a 2nd run, but I'm betting it would cap out around 3-7M damage