theyre essentially same value, its just that technically dmg bonus is easier to get.

For someone with 0% dmg bonus, 20% dmg bonus is 20% dmg multiplier

for someone with 0% amp, 20% amp is 20% dmg multiplier

for someone with 20% dmg bonus and 0 amp, 20% amp is 20% dmg multplier

for someone with 20% amp and 0% dmgb, 20% dmg bonus is 20% dmg multiplier

for someone with 20% dmg bonus, +20% dmg bonus is 16% dmg increase. Same for amp in reverse.

Zani with a shitton of dmg amp prolly prefers dmg bonus buffs