Capstone or Evasion.
How can Capstone compete vs Evasion if Evasion is "elemental damage reduction"?
The only way I see that I'd take Capstone and not Evasion, if I'd lets say get perma File Shield:Cold, Fire, Elec and Earth. All at the same time, and stacking with everything else.
An idea is that you just modify existing effect. That Fire Resistance, Cold Resistance item/spell/potion/etc. It now gives 10, 20, 30,... flat DR vs elements. Change it into 10%, 20%, 30% ...
Caster can cast a spell, anyone can drink a pot (maybe not the best, but better then nothing), get a nice item, slot a gem. It may not be as good as Evasion, but also not that bad. And as Evasion is not for free (must splash class, have pretty high Reflex saves), even I'd think twice before I splash Rogue/Monk just for Evasion.