After reading a couple strategies and planing how to adapt them to my own I gave a last shot, before surrender and train to level 100, to the Golden Mage Knight in Tales of Xillia and pwned him.
before the battle ate something that give +40% physical and arte defense.
first phase, the mage mimic Alvin as the mercenary mage. I played with Alvin and commanded Elize and Leia to only heal and Rowen spellcasting, I centered on knocking the enemy(Dark Radiance and Demon Inferno worked like a charm, Variable Trigger is useful to charge before using the other artes and when charged deal great damage and can stun) to win all the time I could and allow Rowen to cast with ease. linked with Leia for the Spinning Thunder linked arte and also used the hi-ougi on every occasion.
second phase, the mage split into two, duelist mage and conductor mage. I changed to Elize and switched Alvin for Jude and linked with Rowen for his magical barrier assistance, spammed Revive and Nurse when necessary(AKA more than half the fight) and abused of Negative Gate(is great!! sucks the enemy in while dealing damage) and the Azalea Drive linked arte and Elize hi-ougi. first centered my efforts on the duelist mage(Leia clone) because can heal and the conductor mage does almost no damage thanks to Rowen magical barrier.
third phase, the mage split again and now there are 3 mages, the creator mage(Milla), scholar mage(Jude) and puppeteer mage(Elize). I tried to maintain the same strategy but switched Rowen with Milla, things went bad and started to struggle, in desperation used an All Divide, switched Rowen back and started attacking the puppeteer mage because has healing artes. the battle progressed slow and somewhat steady, changed Leia strategy to allow her to attack(but prioritizing healing) to help Jude a little on the tanking/distraction while I was setting Revive on everyone again, once I was done started spamming Negative Gate and Azalea Drive with a occasional Full Resurrection or Revitalize, of course used Elize's hi-ougi when I could. when the puppeteer mage died the battle started to get more or less the same as phase two and centered my efforts on the scholar mage, he is annoying always at your side and sending you to fly. then the scholar mage was finally down and the battle turned into a piece of cake, switched Jude and Leia with Alvin and Milla, I took control of Alvin and the creator mage was gang raped. shame didn't last enough to use the hi-ougi
the battle was loooong, 1 hour. as a note I was playing on hard with double damage activated via ng+.
after that very hard fight the devil weapons where unlocked and continued and finished the last boss with my new found power.
time to play the very first Infamous.