[tom-_-]

"You don't have to write any software to build and manage that production system."

It depends on the scale and complexity of your application. At some scale/complexity, it absolutely requires writing software because your IAAS provider doesn't provide you with automation that covers 100% of your operational needs and even they recommend using infrastructure as code tools to manage your infra.

If your production system is a CRUD service with 3 application nodes and a managed PostgreSQL instance then you do not need to write software to manage it. But if your application is that simple, then I'd suggest you probably don't need a software developer to build it (Wordpress, Wix).

Construction vs custodian is not a fair analogy because their training and evaluation doesn't really overlap. The training and eval for both "dev" vs "systems" engineers is very similar; most have CS degrees and have to do some leet coding to get the job. Devs generally need to be better at algos, systems engineers need better understanding of networking, os, system design.