By the standards of McCall's day, Firpo is an undersized, underskilled powerpuncher with a wide open delivery and little speed to forgive it. He's a poor man's Maskaev.
Were this even true (he could deliver that right hand quickly), you can be all the above, and with a great chin, be a champion powerpuncher. But you can not be all the above and be undersized and slow and devoid of skill.