Software engineering as a field has accomplished so much in terms of quick iterations and low-friction paths to products that I think it has become lost that there are established ways to establish a safety case in a technical manner. Modern software engineers have achieve this speed, largely, by choosing not to apply the level of rigor in process that you describe. This is usually ok, because most software projects do not require that level of rigor (until the costs are too high not to, like AWS, which formally specified critical parts of their infra in TLA+ before software and IT people implemented it).

I think the parent post is an example of this problem taking on flesh. It has been so long since we realized the folly of over-specification in most projects that we have lost memory of there being cases where having a body of people engineering the system and specifications distinctly from the people who implement them actually does matter a great deal.

As a software engineer and not a systems engineer, I thank you for your comment. It has great clarity.