There is some autoremediation in place, but the expectation for responsiveness is top down. Efforts to bring sanity to the situation go ignored. Its been made clear (not directly, but through process) that there are a line of people who could take the job if that level of responsiveness isn't delivered.

There is always someone willing to take your job. Most won't have what it takes. But managers will use that to cow you into a shitty bargaining position.

Look I've been you. I took the crappy job because I figured that was the only one available. There are better companies out there. Just ask around. Get a few offers.

There is nothing normal about being on call with a 1-3 minute response time. I'm pretty sure it's illegal as well.