I’m designing a kineticist and was thinking of going full evil and necromancy direction with void. I’m not a fan of Emptiness so I was wondering with elemental purist can they take the expanded defense and select another defense ability as if not taking that archetype?
No. Expanded defense requires you to have selected a second element through the Expanded Element class feature. As an elemental purist you have traded out that class feature for Elemental Impossibility. Because you dont get expanded element you cannot take expanded defense.