[wedowhatwedo]

Mainframes aren't just about computing power. In a mainframe, almost any component or subsystem can fail with no downtown to the applications at all. That is worth the money and complexity to some people.

You don't understand mainframe systems well if you think they "choke on laughable volumes of documents".

The mainframe isn't the bottleneck in systems like this. It's all the stuff around it that wasn't designed to the same specifications.