Ant's Editor, Anthony Howe's entry to IOCCC '91, surely took him longer than 10 hours to write; David A. Wheeler's "SLOCCount" estimates about 0.65 person-months (because it's 289 lines of code), which is roughly 120 hours. In its unobfuscated form, it's 5065 characters of C, including comments, and not including the curses implementation it runs on. It's a vi clone that's complete enough to use for real work; you could reasonably argue that it is not "of value to anyone" because there are other editors available that are more featureful that can run anywhere it runs. It lacks, for example, yank, put, and undo. But it's definitely featureful enough to use when you don't have anything else.

If you type 90 words per minute of English, which is a speed that most people reach with a little practice, you can almost certainly type C at 45 words per minute, which is 270 characters per minute, 4.5 characters per second. (Jamie's 500 characters per minute is obviously higher than this, but I think he's a faster typist than most.) That would allow you to type in the Ant's Editor program in about 20 minutes, if you were just typing, not having to figure anything out.

20 minutes is shorter than 10 hours. Like, 30 times shorter. If you had everything totally clear in your mind, you could write 30 times that much code in 10 hours.

Now, is it plausible that somebody could write a whole usable text editor without having to figure anything out, so that their typing speed was the main limitation? Maybe if they'd written a lot of text editors previously. I'm skeptical, having spent half an hour getting binary search right last week, but then, there are much better programmers than me out there. (I still find that SLOCCount systematically overestimates the effort required for things; the calculator program with a generic numerical solver I mentioned here a couple of weeks ago in another comment was 261 lines of Python and took me 12 hours, and SLOCCount estimated it at 0.59 person-months, which would be 100 hours.)

I think writing things in very high-level languages like Python instead of C helps a bit, too. Not an order of magnitude, but maybe 2-5x, especially for small projects like these. I wrote a text editor on an iPaq in Python on my honeymoon.

So, while I agree that you're almost surely not going to write a text editor that will steal users from Vim, VS Code, or Emacs in 10 hours, I do think you can write a text editor in 10 hours. You could probably write a significantly more full-featured editor than ae.

Surely the optimal amount of effort to spend on such "learning efforts", which are expected to teach you things but not produce a program for you to use, is neither 0% nor 100%.