The only Eidolon that gave me real trouble was the Shiva twins. Odin and Brynhildr I got on the first try, haven't done any others yet.

Other than that, yeah, pretty much every boss mini or otherwise kills me once before I get the hang of it. I was proud of myself for not dying once when I encountered Enlil and his lil' bro.

Hoping I can repeat this success.