I got DT to G11 very early after he was released because of his kit and tanky stats. I was admittedly disappointed with him. I was running zVader in arena at the time and easily maintaining a top 10 ranking. I immediatly noticed that my defense was a lot worse, as I started dropped much more than without DT.
I also found that death mark didn't proc very often, which essentially results in a wasted turn. He needs some pretty hefty mods too. Keep in mind that his lowish base speed requires some pretty hefty double digit speed secondaries. Couple that with as much potency and protection boosts you can muster and he is a bit of a bear to get top tier arena stats.
All that being said, I am working on him during double drops, but mainly because it bothers me to have an incomplete G11 character, not because I plan on using him in the arena. I do bring him him out to play in GW, but that's about it. I still wish I would have used all of that gear on someone else. YMMV