Is the purpose of this article to say "If you only do one thing, you will likely not excel at other things"? Is there anyone to which this is not an obvious conclusion? Did I miss the point?
You did.
The point is if you let something think about x for you you will become worse at thinking about x.
The purpose of the article is to say that the skill of software engineering depends on the ability to write code by hand, even now that you don't necessarily have to on a day to day basis. If you don't keep in practice, the author thinks, you will become less effective even at driving agents than people who do.
Is that true? I'm not quite as confident as the author, but it seems plausible. I've seen a number of managers who used to write code try and fail to drive Claude as well as even the junior engineers reporting to them.
I think you did. The argument (which may be wrong) is that agentic coding has a lower barrier to entry than hand-coding, and that since (barring AGI) there will remain a demand for hand-coding, that skill will become more valuable the more developers lose it, while agentic coding due to its lower barrier to entry will become less valuable.