Ahah, be more chillax about it
Just look at the ammount of "armor" it gives you.
I have a set that gives insane protection against fire (by coincidence because i was just looking for "armor" bonus) and insane weakness to thunder.
I just keep using the same armor no matter what.
I will have to fight Kirin at some point (thunder monsters) and im pretty sure i wil have difficulties with my armor.
But i will do it either way.
If i find it impossible (which i doubt) then i will change armor. But is not mandatory.
Just chillax and pick what gives you the most armor Leave to pro stuff to when you finish the story.