If we wanted to be a bit more realistic, we'd separate "attacks connecting" from "taking damage" in the rules - so dodging would prevent you form getting hit in the first place, but platemail means you often don't care even when you do get hit because 'ding'.
Dex (and other unarmored defense abilities) would affect dodging and therefore getting hit in the first place (possibly cross-referencing encumbrance), armor would reduce damage on a hit (and if it's reduced to 0 secondary effects wouldn't trigger - ie no poison).
This, of course, adds a layer to the whole attack-roll sequence, which makes combat slower.