You should wear 1 light 1 med for undaunted passive. 5 med is very good for damage and survivability if you mainly kite. Heavy is good too but i wouldn't go higher than 3 pieces.
I wear three heavy three light and one medium. The heavy and light sorta cancel each other out for the negative effects. If I wear an item or have a skill with damage mitigation I typically wear one heavy chest, 5 medium and one light.
I prefer 3-3-1 as it provides higher health pool, slightly better resistance, higher crit and pen.
Yell at zis until they make stamplars viable again
As for your armour question, heavy dies give you a pile of resist, only reason you're seeing the dodge message is called they are using the iframes from dodge rolling to avoid your shots