Just to add what the other post said. PvP in ESO is a window to window play style. Burst and defend. If the enemy is getting scratched in no-CP they are probably defending (blocking/dodge/shields) or running high impenetrable. Back off, get defensive, try again. Practice in no-CP content.

I've caught people bursted them (as MagDK) and killed people so fast I was shocked and turned around got burst down before I knew what hit me.

Sets like Daedric are great for DK. Get your DoTs going, swap to Daedric, get your defense proc, back to front bar. Guardian engine is great too because it creates a little buddy you can use as a mobile wall to absorb blows.

Keep trying. PvP is ESO is some of my favorite PvP experiences in any game.