Is your level high enough? XC is not a hard game, usually it's just a matter of having a high enough level, decent gear and a balanced team... or Shulk, Rein and Dunban
I've never had any issue with this boss with more ether-focused builds (melia, riki, and ether 7 are great). I didn't even realize it was notorious for being difficult until after i had beat the game lol.