I was inspired by this video:

I think this functionality should be removed, with only M1 basic attacks from the 'slinger counting for Forced Penance. Instead Hellshire Iron should be reworked to do the following.

Survivors speared by The Redeemer are Broken for as long as the survivor remains speared. This effect lingers for an additional 45 seconds.

If need be maybe also have the downside that survivor mend time be decreased by 1.5 seconds.