EDIT: your end math is about right (2.59%) but the way you phrase your correction's off.
Yep, it's right between half & two thirds, and I was waffling, changed it a couple of times, and left out the 'two.'
....just doesn't do to make a careless error like that when correcting someone else's careless error!
My original post was just the quote about the number of players and the link, but this is essentially how I read it myself. Indeed, the number that you reverse engineered here happens to match the number provided last time WotC made about the playing audience (about 10 million players, IIRC).
Sorry I didn't notice that was Morrus, I've edited my post, above...
I was intrigued that they straight up said more people are playing now than ever before, that means their market research indicates that D&D is bigger now than the late 70's-early 80's.
Yeah: "“It’s a special time, and I have a big belief that people are really craving face-to-face connections,” he said. “Gaming is the perfect construct.”
As a result, 2017 was “the biggest” in D&D’s 44-year history, Stewart said."
IDK about the Scare Quotes, there, but the difficulty-to-parse bits about growth & numbers came right after that. Maybe "the biggest" is in terms of number playing, or maybe it's sales (before or after inflation?), or maybe it was the fastest growth, even, "biggest" in business speak can mean a lot of different things.
But I'd have to guess the raw numbers playing. 12-15 million just seems unprecedentedly huge to me. In the past, people trying to puff up the hobby have cagily said 'millions of players' a lot, which, y'know, typically means "we're pretty sure we can round it up to 2 million."
But when you've got 10 million or 12 or 15 million, you say it!
WotC doesn't see players without books as freeloaders, they see them as a resource to attract merchandising deals (their real economic goal is t-shirts and toys, rather than game books, it's why they give away the rules for free).
It just feels off that people are playing, but, not, IDK playing 'deeply' enough to want a book... a group of 7 friends where one DMs and he's the only one who buys books, sure, it happens, but the disconnect between selling 750k books, and having 15 million players, that's more like 20:1.
But, yes: 5e doesn't have to sell that many books to turn a profit, and even if it did sell that many, it wouldn't be a whole lot of money, not compared to getting people to go see a D&D movie the way they go to Marvel movies, or whatever they're hoping for.
The 'freeloaders' still generate buzz for the /brand/, even if not revenues for the game, but, wow, there seem to be a lot of 'em.