There are some really strong Mag DK builds in no-CP, as long as you don't mind utilizing proc sets (which almost everyone does on all classes). It's not at all uncommon for the #1 damage on Battleground scoreboards to be a Mag DK in something like Grothdarr and Overwhelming Surge, and their self-healing tends to be pretty decent compared to most other Magicka builds. There's at least one player on PC-NA who's able to spend virtually 100% of his in-combat time either perma-blocking or Mist Forming, while procs keep the damage rolling; for some builds it's basically a straight up hard counter in 1v1.