I have 3 chars now, a heavy shielder, a "pure mage" as in no shield and a short sword, and a cleric with "balanced" attributes.
The shielder is an absolute beast in PvP. I am not that good, I don't use sophisticated tactics or anything, I just facehug and nail my enemies in the ground. Since I passed lvl 50, I haven't lost a single PvP encounter.
seriously. Armor is 26 on average, black tower shield and a brigand +7 axe. If they are being smart with parrying/kicking - I use shield bash. Have almost 1400 life, so even criticals don't take more than 1/3 of my bar.
Might change later in game, but so far, I don't see how a Mage can 1 on 1 my shielder. That's just pretty much impossible...
Hope there will be some very powerful magic spells later in game, as it just not working in PvP
Btw, the best PvP spell I have used so far is farron sword, or whatever it's called, it needs 23 intelligence, but that's the only useful spell in 1 on 1 imo.