> A junior developer has no such skills. Their only approach will be to run the code, test whether it fulfills the requirements, and, if they're thorough, try to understand and test it to the best of their abilities.

This is also a supremely bad take... well, really it's mainly the way you worded it that's bad. Juniors have skills, natural aptitudes, as much intelligence on average as other programmers, and often even some experience but what they lack is work history. They sure as hell are capable of understanding code rather than just running it. Yes, of course experience is immensely useful, most especially at understanding how to achieve a maintainable and reliable codebase in the longterm, which is obviously of special importance, but long experience is not a hard requirement. You can reason about trade offs, learn from advice, learn quickly, etc.