Should i try to inflct on boss more often?

Hey there, i was wondering if the inflict on enemies more useful or just pointless to use. I mean, i am struggling on how to defeat the boss in chapter 11 and i try inflict to avoid getting Mastro from increasing its percect for powerful Soul Cannon. Is there any other tool on how can i defeat the boss Maestro through SP any means. Let me know your comment.

Sorry for my poor English.