Agreed, in my experience, rule 5 should be rule 1. I think I also heard it said (paraphrased) as "show we your code and I'll be forever confused, show me your database schema and everything will become obvious".
Having implemented my shared of highly complex high-performance algorithms in the past, the key was always to figure out how to massage the raw data into structures that allow the algorithm to fly. It requires both a decent knowledge of the various algorithm options you have, as well as being flexible to see that the data could be presented a different way to get to the same result orders of magnitude faster.
I have seen a huge decline in data first over the past decade-plus; maybe related to a lot more pragmatic training where code-first and abstraction helped you go faster, earlier but I definitely came of age starting with the schema and there are an awful lot of problems & systems that essentially are UI and functions on top of the schema.
I don't think they were ever meant to be in order of importance.
I think you are referring to:
"Show me your flowchart and conceal your tables, and I shall continue to be mystified. Show me your tables, and I won't usually need your flowchart; it'll be obvious." -- Fred Brooks, The Mythical Man Month (1975)