You honestly don't understand a Sentinel. Less survival? You do realize they have same values/caps as a Scrapper right? Honestly resist sets on a Scrapper are never best option do to cap of 75%. Unless it's Radiation Armor(That set just OP in general). I have Electric Blast/Rad Armor Sentinel that fucking scary. I have other types to. When it comes to defense values, everyone soft caps at 45% thus granting 5% chance to be hit by a mob. Before any debuff/buff is factored in.
As for your Blaster reference, that's ok. They have one thing a Blaster does not have. Status Protection toggles. Blaster would murder your children for that option. So of course they won't have high end dmg. It's called a Trade Off.
They are fine. Just a ranged Scrapper without the crits, but with bonus of being ranged. Honestly, I see a lot posts like this(not just on Sentinels). By folks who don't either play test, don't recipe up, don't understand, etc.. Just assume and then talk about it.
Also this should be in Sentinel forum.