I really dont see much Defender Titans in PvE. The whole Class is imo far from its D1 Glory. In D1 a Bubble Titan was a very good Choice in many activities, in D2 this subclass is mostly ignored.
What can be done to make it great again ;) ?
Get back Weapons and Armor of Light
Lets shoot trough the bubble (from inside to outside) - the damn Cabal can do so too. I shouldn't be a Problem