If the old damage calculation thread is anything to go by, that’s not exactly how it goes.
Damage ≈ 100 x ( θ x Att / Def ) ^ 1.35
Let’s assume θ averages to 1, and look at a few possible defense ratings vs Cap’s 724 attack @ 260%, Morel’s 946 attack @ 180%
Defense 800
Cap: 227 damage (240 post-buff)
Morel: 226 damage
Defense 900
Cap: 194 damage (205 post-buff)
Morel: 193 damage
Defense 1000
Cap: 168 damage (178 post-buff)
Morel: 167 damage
So… essentially identical damage pre-buff, interestingly, Cap slightly ahead after the buff.
Morel actually hits all, whereas Cap chains through folks with minions. Of course, one point is that Morel’s niche (applying DD) is a wee bit broader than Cap’s (removing minions).
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My greater point, though, is that the damage of either hero is not the relevant point anyway, it’s their special effects. Buffing Captain of Diamond’s damage by around 10 hit points is pretty arguably not particularly meaningful.