Which legendary does more overall dungeon damage? Assuming you spam both off CD and your PI is always casted on your highest DPS
Twins.
Damage to tanks is too high in high key to use Penance for dps, so you will mostly defensive penance.
Even in a universe where every Penance is used offensively, it’ll still favour Twins and it won’t be close.
Normally you are setting your PI up on a dps during a larger trash pack. They overall dps that the dps can do during that trash pack will outweigh easily a few penance bolts. Lets alone the 2-3k dps YOU can do on that pack too
I’ve tried both in mythic situations and favor twins even though I hate it as a leggo. I rarely used penitent one offensively it was a great defensive heal for the tank though and I could cast it while moving