Originally Posted by
Shaiandra
If we assume Hu Tao has 46.6% Pyro from her goblet, 15% from 2p Crimson Witch set, and 33% from her A4 passive, that adds up together to +94.6% Pyro damage, so she's already dealing 194.6% of normal. Mona's +42% is additive to that (all DMG bonuses are), so that would instead make her deal 236.6% damage, and comparing that, 236.6/194.6 = ~1.2158, which means Mona's EB is adding about 21.6% damage.
Whereas if you don't have any resistance shred already, adding Zhongli's 20% shred will also add 20% more damage (assuming the enemy had 0% pyro res to begin with) since resists are another multiplier (not additive with DMG bonuses), hence being very close to the above. If an enemy had positive Pyro res, this effect will probably grant even more than the 21.6% of above.
Long story short, I say Viridescent Venerer has the strongest set bonus.