Rather than analyze all the reasons why a suit would probably fail, how about we pass the immunity, get the surveillance, and save the legal analysis for elsewhere.
If Congress wants to provide a surveillance environment free from the risk of civil suits, it should repeal the laws that enable those suits. No such repeal has been suggested by either the administration or the Republicans in Congress. Yet civil suits relating to surveillance ALL have the risk of disclosing government secrets. So why have a statute that give a right to sue?
But what prompted me to post at all was your comment:
The telecom companies did nothing more than provide assistance in accordance with a law passed by Congress.
I wonder if your conclusion would change if that assertion was false. I happen to believe that it is a false assertion, but I certain have no interest in disabusing you of holding otherwise. Still, I don't think it's an unfair "hypothetical" to those who believe that 100% of the government's surveillance has been conducted in accordance with a law passed by Congress.
If the telecom companies broke a law passed by Congress, do you still think it's appropriate to "pass the immunity and save the legal analysis for elsewhere?"