It would make the penance feel a lot less arduous, you wouldn’t need to change the description much and it would prevent a lot of the terrible behavior from players chasing the penance.
Also, it would be nice if it counted deaths from the flame barrels as well - i’m pretty sure it isn’t doing that currently.
It seems like the penance is balanced around difficulties 3-4, where explosive barrels can 1 shot trash mobs in a much larger radius than on damnation difficulty.
It is much more difficult to farm explosive barrel kills on damnation, despite more enemies being present.
That seems like a bit of an oversight, which would be less of an issue, if flame barrel kills counted as well.