is dragon smithing worth it ?

how does steel fist perk work because ive been testing smithing + heavy armour with out saving after and i can then boost the dragon gauntlets to have 240 armour rating (its like 180 base legendary smithing it doubles and then enchanting a ring gauntlet plate body and necklace for fortify heavy armour gives me 200 in heavy armour) so would i really be doing up to 240 damage in melee ? (i mean i did run around with it seemed fairly useless against guards but every un armed non hostile npc i came across = instant kill cam (and some of them were just brutal)

also why do you need 100 smithing to make dragon if Daedric armour has a higher armour rating

(in the craft select i highlighted over a daedric main piece an was 97 armour rating i then went to dragon main piece and was only 91)