Penetration should just be capped like armour and spell resist, which would mean that even light armour wearing players wouldn't get hit as if they were running around naked. Just make it 50% max spell penetration, I mean it is only possible to reduce damage by 50% with capped spell resist and armour, so it'd make sense.
Also, you might say that the healing taken buff is useless, but trust me that stuff stacks really nice. I can heal about 75% of my missing health with Coagulating Blood on my DK by using 5 pieces of heavy armour Eternal Yokeda (5% + 8% increased healing taken), 8% from Coagulating Blood buff, 30% from Igneous shield, 10 points in Quick Recovery (4% increased healing taken) and 100 points in Blessed (25% increased healing done). You might say that the 5% from my 5 pieces of heavy armour doesn't matter, but with all this other stuff I have going on it really does. I will also point out that not every pvp player in the world has that high an amount of penetration, a lot do, but not everyone. Heavy armour really isn't useless in PvP as you think
The reason heavy armor still sucks terribly:
http://forums.elderscrollsonline.com/en-GB/discussion/148766/heavy-armor-is-so-op-in-1-6/p1
Many people start to shout in blind panic when any form of balance is applied.
"In all honesty, plate still has crap resource management.
With the softcaps removed, our lack of resource cost reduction will make a severe difference, as well as the vastly improved regeneration other armors will have.
We get a tiny amount of both magicka and stamina once every four seconds. Whoop whoop. We get nothing that benefits our damage. Our reduced cost for breaking free has been removed from our passives, our damage increase has been removed from our passives.
We have a whopping 7% health increase and healing taken increase. Aside from that all we have is our armor and magic resist. (which in PVP can quite easily be lowered)
Plate is probably still laughable, just like the cloth/staff people panicking that their armor is no longer better at -everything- "
Heavy armour really isn't useless in PvP as you think