I'm quite a new returnee, and this question has been bugging me. I can't figure it out on my own, so I'm asking you experts.
Considering IOs, I can get reasonably good on defenses with a Blaster. Yes, they are lower than what Sentinels get, but not by much in actual practice. But a Sentinel's damage is far worse than a Blaster's damage than the defense comparison.
Admittedly, I don't really understand Opportunity. Maybe that's what I'm missing? What's the story with why someone would pick Sentinel?