All of the companies that would instantly start losing a billion dollars per second would never allow this to happen. This isn’t some 3rd world country where Google and Apple and Facebook aren’t headquartered. The internet will always be happening here. They’re completely dependent on it and their customer’s constant access to it.
Our econnomy is heavily tied to the Internet at this point. Billions in commerce are conducted directly and many billions more in enabled ("what's the closest pizza place?"). Not to mention stock trading, banking, government services, healthcare, etc. You're very much on track here and I don't think it's hyperbole.
While it could technically happen that our government could legally shut down the internet, it wouldn't last long or it means we are under attack (perhaps internally) and need to control damage/messaging.
The alphabet agencies are fully capable of doing whatever is needed, they’re the ones that patch peoples systems for them or hack PCs through the power grid and other crazy shit.
If the American government wants the internet to be cut off they’re capable of doing it without the assistance of the ISPs