since we already have any damage reduction effect not stacking and only the highest effect will be applied, why not also implement this with the evasion? that way we would reduces issues with stacking ml cartuja's passive ,violet's passive, moonlight dreamblade artifact, violet talisman artifact, and so on.
So you want to kill Violet? If it wasn't for these evasion artifacts he wouldn't be nearly as relevant as he is now. Besides, dmg reduction is, as you say yourself, an effect. Evasion is a stat jsut like counterattack chance or dual attack chance hence why they add up.