I don't think I need to be reading this. The uptime and several 9s of high availability are attainable with z/OS and a parallel sysplex. No doubt systems like these are used by banks and others in the wild.
But this doesn't say anything about "unbelievably powerful" or "feature-full" as in the OP?
The niche customer claim probably is "will never move off of it because nobody ever wants to touch millions of lines of COBOL" then that's fine. It's likely sane from a business perspective to continue using them as long as maintenance burden is manageable. Luckily managers in those more conservative companies consider full rewrites dangerous, rightly so.
But in order to claim otherwise (i.e. unbelievably powerful and thus for everybody) we need to see numbers.
I’d say 15+ years ago, they were very powerful relative to other solutions on the market during those times. But I agree that’s no longer the case when compared to modern server racks.
I pointed out that Redbook about HA features since it’s a major differentiator of mainframes even today, but there are also these that document other features:
You can find 1 or more books that go into a deep dive of every chapter.
IBM has taken input from the biggest companies in the world over many decades to run as many of their workloads as possible. They’ve honed everything in their software and hardware to do so, down to developing specific cpu instructions to support specific use cases. If all of this doesn’t convey an extremely feature rich system, I’d like to hear why you think otherwise.
But this doesn't say anything about "unbelievably powerful" or "feature-full" as in the OP?
The niche customer claim probably is "will never move off of it because nobody ever wants to touch millions of lines of COBOL" then that's fine. It's likely sane from a business perspective to continue using them as long as maintenance burden is manageable. Luckily managers in those more conservative companies consider full rewrites dangerous, rightly so. But in order to claim otherwise (i.e. unbelievably powerful and thus for everybody) we need to see numbers.