Would need to bump up Def a lot IMO. If you took a Fortitude: Sacred armor 1815 vs Dusk Shroud 1416 or 400 def which translates to roughly 2K def after you add Holy Shield. At 18K vs 20K, 2K is not that much of a thing.
Perhaps if the heavier armors were more like 10K diff at those high ends. More over if they add DR to the heavy armors it would add a function that would help.