My stance on quality versus quantity keeps evolving. Essentially, books take as long as they do--when I'm on my own, a book takes anywhere between six weeks and eighteen months, though the birds book seems to be breaking the record, and so does the other WWII book. I understand why these two are "slow books"--they are both historicals, and it drives me crazy to not know enough, to not know a certain detail that none of our "witnesses" have bothered recording and no historian appears to have had an interest in. So for somebody who hopes to make a living of Making Shit Up, I'm really dreadful at making shit up. Making shit up is my least-favoured option after I've exhausted all others. I'm terrified of making a mistake, even though I know that 99% of all readers likely know a lot less than I do. It's the 1% I'm scared of.
So, yes. Slow book. Research slows everything down, so a fast book is usually a contemporary. You do have a good grasp of your current world, after all, so the research is often minimal. Considering that contemporaries outsell historicals and every other genre by at least a factor of 5-10, you gotta be stupid to write them. Stupid, or just love the book too damn much for your own (financial) good. Thank gods money isn't everything, though it's a real factor/consideration for those of us who rely on writing for income or hope to quit our dayjobs so we can write more.
So from the point-of-view of writing a book for 18 months and then waiting 2 years for its release (this is 12 years ago or thereabouts), I once read an interview with Germany's most beloved pulp author, who writes 64-page pulp novels (really only novellas); the whole series by now has something like 1,500 issues, and most of them were written by that one author. According to that interview, he writes 25 pages a day, which, depending on your page/work count, is something like 5-7k a day. With 100k readers, he's popular, and I was collecting those stories too (for about two years, I think). Essentially, with a weekly need to deliver, you grow very, very, very disciplined.
While Rellergerd (the pulp author) is doubtlessly one of the most productive authors I know in Germany (the other very productive YA author uses 3-5 friends who publish under his name to reach a similar wordcount), he's not the only one who has a huge output.
La Nora herself has written 200+ books. I've tried looking up the Most Productive Authors, but then got lost in the internet, so I'm making my argument without it.
When I switched over from "mainstream speculative fiction" to write m/m ("original slash", in some quarters), I wrote some things and they didn't really go anywhere because I wrote them just for fun and had not a hope they'd ever get published. No deadline, lots of other things I was doing = low total wordcount, and nothing finished. Then I wrote Special Forces, which is roughly 1 million words. Let's say my part of that is 500k words written in ~2.5 years. HOWEVER, that's not much, actually. It's roughly 600-700 words a day.
It was mostly written fitfully--many, many words on some days, none on others, which is still pretty much how I write. I do nothing for a week and then have an amazingly productive weekend where I write 4k. I used to calculate "one chapter/week" for anything that had a deadline, and that worked, since a chapter is anywhere between 1,500 and 4k words (though recently I've done micro-chapters which run to 4-5 pages each). I've co-written a historical novel in 4 days--a feat I'd have thought physically impossible, but then, it's just 8k a head a day. Never mind you're emotionally and mentally flatlining for two weeks after and then need a month or so to edit. It's still a novel in six weeks. My physical limit by myself is roughly NaNoWriMo - 1,667 words/day, which means 2.5k days and 5k days and 400 words days all jumbled together, and wanting to kill myself with a spork towards the end of it.
Every book has its own rhythm and speed, too. There are fast short stories (one day). There are slow short stories (2 months). There are fast novels (4 days), and slow novels (1.5+ years). The main difference between "fast" and "slow" for me is genre (historical/specfiction versus contemp) and motivation. (Health, too, though I'm young enough to assume right now I'm mostly physical able to handle the strain of sitting front of the computer for a long time, unless I wreck my back). This might not always be so.
So, returning to my original point. There's sometimes the opinion that writing fast means writing badly. And on dark days, I might catch myself at times wishing that were true--some days, I just envy authors who can write a novel in ten days, because damn, I can't, and damn, they actually have a chance to keep up with all their bunnies and ideas for stories. They don't have to do that merciless triage of "Yes, I'll write YOU, but YOU, you go and die, I have no time for you." So when I see people constantly writing a book a day, at the very least PLEASE GODS LET THEM SUCK. But they don't. The crazy thing is, speed and quality are not correlated in the way that some people think.
I've read books that took 10 years and went through a gazillion drafts, and they were amazing. I've read books that took 10 years to write and they were bad. Like, really bad. So bad you'd want to put it out of its misery, and the poor author, often a hopeful debut author, who tells you that they worked "hard for ten years on this--this is my magnum opus", and you read it (usually online) and it stinks. Not only that, the author hasn't learnt any technique. The author might think that just by virtue of the length of time it took to make, it HAS TO BE GOOD. But it's not.
The difference between a good book and a bad book (we're talking about craft) is not time, and I don't even think it's talent (though talent helps), though in the truly remarkable authors, it's usually there. It's training. A properly-trained author applying him/herself in a diligent, disciplined manner will always outwrite a "happy accident writer" who "felt like it, but not today, ah, no, not today, either, maybe next week, and oh, shiny!" if both have a similar amount of talent and skill. At least that's true at the start.
The truth about very productive authors is that "practice makes perfect" (yeah, that old chestnut). So they write five novels in the time it takes a slow writer to write one. The payoff for being productive: with every completed story, you learn something. Writing five novels, for example, teaches you five different things you can apply to novel number 6 and the ones that come after. Every book teaches you how to write it. The more you learn, the better an author you'll become. The cleaner and more mature the style, because upholding an artificial "auteur pose" (aka: artificial, self-conscious style) is really fucking hard when you're writing 60-100k a month. You can't do it the same way you cannot run a marathon in ten-inch heels. Eventually, the sheer speed rips away all stylistic pretensions, and what emerges is--not your ugly true self, but your Voice. The one that's natural to you. Because that's the only thing left when you work at that speed.
I'm not saying what is written that way is always publishable. Editing is a totally separate step (gods save us from the "published first draft"), but once the text is there THERE, it can be edited. We all need editing, anyway, and much more than most of us are getting. A truly great author is one who edits well--who can clean up that draft (whether written in ten years or ten days doesn't actually matter) and turn it into the best thing it can be. For many, editing takes longer than writing it in the first place. But that is okay. I'd even expect it in a fast writer--it's what I've seen and encountered in my own writing, though by such standards, I'm an author who writes fitfully, but consistently (= medium productivity).
So, slow writers, relax and let it flow; the story knows what it's doing. Fast writers, don't be ashamed of being fast or getting flak for being fast. I'll see both of you in edits, where the book really happens.