I found him to be really tame with a 45% atk/mag break. You can use WoL or Ling for that. 9S has 50% breaks but his are split atk/def and mag/spr so you'll have to use two turns to fully break his offenses. I don't think Sol ever uses Erase(Seriously, why isn't there an erase spell for healing yourself of breaks. This was a core mechanic of the damn spell in xi) on himself.
Maybe there's more to the fight than that? Don't equip light weapons and you should be fine as long as you're all leveled up iirc.
I personally found Behemoth a lot harder going in blind.
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