> It has all the downsides

Vendor lock-in from a single vendor? Wildly expensive capex and opex? Impossibility for people to know any of the tech involved without you sending them on a course to learn about it or them already having experience with it?

> Try to write AWS Lambdas that call each other within the same transaction.

Why is that your comparison? Was deploying to the mainframe as simple as throwing a .zip with your code at an API that you could give access to developers?