I know plate mail gets more defense but does it protect you better

the only real protective difference is defense...
now if you have a 100 ee chain mail ofc its gonna protect you better than a 0 ee plate mail... theres no real difference other than the defense, and orfc whatever stats it has on it

Defense is the protection you recieve from melee non critical damage

eg: Monster rolls a 100 melee damage non critical hit your defence = 25 to 35 so the net damage you would take = 65 to 75