Well, he begrudgingly went Ares for a few reasons. First off, he knew he needed more strength. If he did go any more defensive, his martial arts style would honestly lose effectiveness, as most others would be able to force themselves out of his grapples. Second, his fighting style lends itself extremely well to one v.s one combat. Lets say, for example, he faces multiple foes. Even without Aries debuff, he'd still lose, as he'd not be able to properly pull of his moves, which requires him to remain pretty much stationary, as he works to snap a limb using leverage, or by constricting vital points to slow the flow of blood to the brain to know others out. But, in a one v.s one situation, he's extremely potent, breaking his foes limbs to render normal fighting styles difficult.
Also, he's trying to prove something. A warrior may need to fight...but to fight, without killing takes strength greater than what most warriors have. This is what Cran believes.