[ninefathom]

I can second the legacy and reliability assertions. My experience with z/Arch was more recent- and it's a very different world from the modern cloud CI/CD Linux git Dev[Sec]Ops thing- but the reliability and legacy support immediately impressed me. A single z/Arch rack is basically a cloud in a box - get it power and network connectivity and you're golden. Other vendors can offer that though. The legacy support is another story; I watched an NGiNX proxy and a custom financial reporting app from the late 70s running side by side on the same box, and that's when I understood the additional dollars.