Your argument is invalid simply because..
a. archers kite
b. warriors armor crutch
c. warriors armor crutch because of archers
d. therefore, archers will always kite unless warriors stop armor crutching.
Archers have no need for armor, so they wear barely any. also, a lamellar coat has 36 body and 9 weight.
+3 would be... 40 body, 5 weight, according to your suggestion?
if anything, i think having any armors under 7 weight having more than 25 body is a mistake; they should all be weaker. i think that everything that comes after surcoat over mail should be buffed so that warriors can wear lighter gear, to chase lighter troops, or heavier gear so that they can stay away archer fire and fight right on the line.
as for heirloom changes... they should have MORE weight technically, since they are being reinforced and strengthened. i suggest that armor gains +1 armor, and +0.5 weight per loom.