But that's what I mean. A person can take 20 years to write a book because they write 15 words a day, every day, for those twenty years. Or, because they write like a mad man for a few weeks, then let the manuscript sit for four months before returning to it for a few more weeks. Or, because they have an incredible skill set to begin with, and they take that much time to craft the prose, plot the story, and fully develop the characters. Or, everything in between those three scenarios. There are too many variables not accounted for.
Length of time alone doesn't take into account anything else. Saying it took me 10 years to write a book doesn't necessarily mean I wrote every single day, with a consistent word count, for ten years. It's nothing more than a measure of time, without any details of how much talent I had to begin with, how much I understood the basics of plotting and character development, how many words I wrote each day, whether I even wrote each day, and how much time was spent going back and self-editing.
Concluding that if a person took more time with a particular book, it would have better plotting, character development, etc. isn't necessary true, because that person might have written the book in the best way they know how to. More time wouldn't give them those skills if they don't understand what's missing in the book in the first place.
Taken by itself, those three months, four years, ten years, twenty years, means NOTHING. And that's why I don't care for blog posts like that one. They're misleading, and the information isn't really useful. I can't stack up those amounts of time against how long it takes me to write an average book and say "See there? So-and-so takes this long and so do I, so that must mean my books are as bad/good as theirs!" There's no real correlation because there are too many variables not accounted for, including a skill set, or lack of, to begin with.