When people complain about oncall, the off-hours portion is almost guaranteed to be the part complained about.

Furthermore, I'd argue that if there is a dedicated group of people whose job it is SOLELY to work outages and help tickets, and their job is 100% that, it's not oncall.

Oncall is "hey, you have these projects to do, but every 6 weeks you have to also answer every IM/phonecall/ticket escalation as well".

Yes, I worked at a company where tech department was severely under-manned, and we had to be great at "SRE" type stuff. (I will definitely be reading this book, I even applied for this SRE position at Google while I was still working there...)

The number one problem was that (starting in Year 4) there was nobody else with the knowledge to be on-call. So, I was on-call 24/7-365 for 5 years. Realistically it was a small enough company with localized (mostly east-coast USA) clients, that things going wrong in the middle of the night was pretty unusual. I had a great boss who mentored me to be able to handle these things by myself, and he mostly put the right tools in my hands so that it was possible to avoid getting woke in the middle of the night because anything went wrong short of a disk going bad.

It happened often enough to be a good reason to want to leave! It was my first serious job, and for all its faults it was a pretty great job until my boss got a better offer. When he left, it seemed that there was no choice but to implement vSAN and VSphere. And then I actually didn't need to be woke by disks going bad in the middle of the night anymore.

When I did go, there was nobody prepared to handle 75% of the incidents I would have been needed to work on. (I assume that many of those things just stay broken now when they go wrong.)