A crit on leverage can do more than a non crit flurry. remember, flurry isn't guaranteed 4 hits and to get maximum damage from flurry, you need buffs like offense up. if she has any debuffs at all, she loses offense from her unique.
To get the hardest hits out of her, you need to carefully buff her up.
You're meant to get foresight from her basic, then offense up from using leverage with a buff, then use leverage with offense up and advantage for a guaranteed crits. That's how you get the huge damage.