Isaac has fought creatures that are comparable to the Flood from Halo a dozen times. Hunk's biggest feat is surviving an attack from a monster most of the Necromoprhs Isaac's fought would eat for breakfest. Not to mention Isaac has superior weaponry for his weapons shoot plasma which will eat right through HUNK's protective gear and kill him instantly. HUNK's weapons might as well be BB guns since not only those are laughable in comparison to plasma weapons but the rounds from his handguns and SMGs won't even pierce Isaac's armor.