Is source code really the actual design of a software product?

Our beloved software design and programming activity is about 50 years old and that counts as a drop in the ocean of the history of a well-established and well-understood human endeavor (a very adored drop indeed).

One useful thing to do, as always, for the advance of our profession is keep questioning, reflecting and learning about what we do.

Perhaps these essays could help better understand what "source code" is and the relationship between design and implementation activities:

1-What Is Software Design?
2-What Is Software Design: 13 Years Later
3-Letter to the Editor

Code as Design: Three Essays by Jack W. Reeves
https://www.developerdotstar.com/mag/articles/reeves_design_main.html
https://c2.com/cgi/wiki?TheSourceCodeIsTheDesign

Also, look at Component Software by Clemens Szyperski ISBN: 0201745720, there is a very interesting exposition about what is and where the design of a software system resides.

Some people get very angry with these concepts, to lessen the problem please keep in mind that “source code” could be an abstract notion with many concrete derivations.