No idea, I've never beaten the game.
That Barthandelus fight was pretty crazy. I tried it once and spent over 20 minutes trying to beat him, only getting him down to about 1/3 health. Then he cast death on lightning so I switched to relentless assault in a desperate attempt to beat him, and just got killed.
Second time around I switched up my paradigms - I used Smart Bomb to afflict him and buff me, delta attack to stagger, relentless assault to work his stagger meter up to 500%, then aggression until the meter ran out.
Ended up getting 5 stars the second time around.