It is not like endgame pve where you need a certain standard stats, specific skill setup, specific weapon for role, to be top notch.
In pvp penetration is not as good as in pve, because magicka players use Magick shields and pen will not work on those. If you want to do more dmg vs higher res stacking players then you go for more pen and the other way.
Pen will also not increase your healing done.
On my stam nb I have, I use major fracture+ 2h maul atm, plus 2-3k if In cp.
On the Sorc I play almost nothing in pen.