Sure, blasters can do more upfront damage, but if something so much as looks at them the wrong way, they have to pull back from the fight. And if there is a bad pull, patrol, etc., they are often the first to hit the ground for a dirt nap.
I've actually re-rolled blasters as sentinels for the express purpose of being *more* useful to team fights. By being able to stay alive a lot longer, and taking stress off of the healers, you do more damage over the length of the battle without being a burden to your support. I can't count the number of times while playing as a sentinel, I've been one of the last ones standing, alongside the remaining tank, while the blasters have either run away or have been incapacitated, their potential damage output having been lost long ago.
As a sentinel, you can stand your ground, and keep shooting, whereas, as a blaster, you're having to re-position, retreat, and try to make some use of your secondaries--many of which serve to make you more vulnerable. As a sentinel, your secondaries are always useful, especially to the healers, who can let you take a few hits while they concentrate on keeping the blasters, scrappers, etc. alive. Work in some powers from the Fighting and Presence power pools, and you can easily play as an effective bodyguard for your more fragile teammates.
It's too easy to just pass the sentinel archetype off as some kind of second-rate blaster. Because fights in this game--especially at higher difficulties--can always get sloppy, there's almost always a need for more people to take the punches than not. And on boss battles, or any fight that isn't against trash or easy 'con' enemies, offensive opportunity is most definitely useful.
