No, this is just an extreme example of the "don't try to be a smart guy" ideology. In practice 100-500 LOC per day is normal.
It is not. You are not writing a novel here. Yes, most of the time is spent thinking. Some days there is no coding because it is spent on just trying to figure out what to do.
I personally don't spend much time thinking about software-related problems. At the risk of sounding conceited, I'll admit that most problems I encounter are pretty straightforward. Five minutes of uninterrupted thought is more than enough to get into diminishing returns.
It would be very interesting if GitHub pulled an OKCupid and published some statistical analysis of programmer behavior. They could put many of these disagreements to rest.
I'm not that experienced, but I had a notable experience working with a 5000+ loc app that was a nightmare to maintain and extend. The last guy had basically reinvented every wheel. He was even, in my opinion, reimplementing the DOM in places with absolute positioning. Also, the code was poorly organized, with pieces of logic that could have been easily consolidated appearing throughout the app in multiple places so that they could not be abstracted out.
After about a month of trudging through his code and making almost no progress, I basically told my manager that we had to rewrite it (I had been thinking this the whole time, but I didn't want to be the junior dev who comes in and demands to scrap everything).
Me and a colleague paired on it for about 2 weeks and rewrote the whole thing entirely from scratch, leveraging several open source libraries and writing a few tested "internal libraries". The whole thing ended up being around ~800 loc when we were done, and it had the extra features that needed to be added, and was pretty bug free.
I'm not trying to blow my own horn here, in other instances I have spent way too long pondering about code and making it way more concise than necessary.
But unless you are a truly great coder who is cranking out 100 lines of good code per day (and I have no doubt that you are), I would be pretty suspicious about the amount that you are writing. I would worry that you are placing a great maintenance load on those who come after you.
Computers have fascinated me since before I can remember. I spend most of my waking hours in front of them. I've been honing my craft for over 20 years. I've written and maintained projects in C, C++, C#, Java, JavaScript (both browser and server-side)[1], Perl, PHP (we all make mistakes), Python, Ruby, and a couple Lisps. In my travels, I've discovered and reported bugs in popular software such as Firefox, Chrome, Node.js, Apple's XNU kernel, and libxml2.
I completely agree that some programmers are like machine guns, firing off vast quantities of poorly-aimed code. I try my best to avoid that. I hate sloppy code. I hate repetitive code. Most of all, I hate re-inventing the wheel. If a decent library exists, I'll use it. I have no qualms with something Not Invented Here.
I pair sometimes. I do code reviews often. And I use as many profiling, testing, and static analysis tools as I can get my hands on.
It sounds like your ordeal made you a better coder. Those sorts of experiences are indispensable, but I've found it takes more to keep improving. It's very useful to become an expert on programming, not just an expert at programming. There's a growing body of literature to aid anyone interested. McConnell's Code Complete is still great. Michael Feathers has a book called Working Effectively with Legacy Code. It contains some great techniques for incrementally improving hard-to-maintain projects. Lastly, browsing It Will Never Work in Theory[2] is a good way to stumble into some academic papers that apply to your own work.
1. "JavaScript" is such a nebulous term these days, but I've worked on JS codebases using tools ranging from nothing (vanilla JS) to JQuery to Google Closure to React.
I can't imagine anyone sustaining 100 LOC/day over the long term unless they think that cranking out HTML templates or something counts as programming.
For reference, I count myself as writing about ~40 LOC a day for a greenfield project (which I spend about 50% of my time on), measured by total codebase size.
And no, it is not HTML templates, although it is a fairly verbose language. And I do all the things you describe in your first paragraph.
In my experience, a good programmer is almost always a fast programmer, and non-trivial programs usually require a lot of LOC to get the job done.
I do this for remote sensing, and I might write 50 loc on the main thing, and often a bunch of python to test if the idea works.