The argument is that the modern software system has become so complex, worrying about what the intent of the original design is almost pointless. Say a single-user app that was originally written in assembly for PDP and has now evolved (or wrapped) into a multi-cluster, multi-zoned gRPC service - how important is the original intent when it was never designed for the current use case?

If you want to do good engineering work on a complex system, it's imperative to understand and remain laser-focused on what the system as a whole is actually trying to accomplish. The original intent is never irrelevant in that context. In fact, it's the foundation for evaluating all the subsequent decisions that resulted in "a multi-cluster, multi-zoned gRPC service".

Sure, but why do we hold the Founders in a particularly high regard? Instead of, say, countless 20th and 21st century politicians, scholars, and technocrats who have a lot more influence on the government as it exists today, most of whom who don't have views nearly as revolting as the Founders.

Who's likely to be able to bring a software system from 16.7.1 to 16.7.2? The team who built 16.7.1, or the team who wrote the pre-alpha version twenty years ago?

In many cases (including, I would argue, the current American political system), the people who wrote 16.7.1 are merely technicians without any coherent vision for long term purposes or principles. Why do we still talk about the Unix philosophy?