Then how do you do it? There are only a few measures of quality. You can look at the editing, which overall is excellent. The layout and presentation which was always good but is improved in the 2024 edition. The physical product, which WotC has little control over, has had issues but when I received faulty books all I had to do was send them back to be replaced. They were replaced quickly
and they also sent me an additional product as compensation. So by those measures, I'd say it's a quality product.
Beyond that? How well does the design hit it's goals? While it's in a nice market, it is a game designed for broad based appeal and a game that most people want to continue to play year after year. That's where ignoring popularity is just smacking yourself in the face to ignore the obvious. It's not just that initial sales were good, every version of D&D has had that. It's the number of people that keep playing the game and the number of new people that also choose to play. We measure that how? By popularity and sales, the fact that the game has seen year after year of double digit growth and dominates the industry. There is no other way.
You like to say that McDonalds isn't any good. Except I disagree. As a fast food (which will never be healthy fine dining), their restaurants are clean and well lit, their food is consistently prepared and relatively cheap. You go to a McDonalds and you know what you're getting. But D&D accounts for 70% (
1) of the playing D&D on Fantasy Grounds. McDonalds doesn't have anywhere near that kind of dominance in the fast food industry, they're #5 for sales per store (
1) out of the top 5 fast food restaurants. Of course the restaurant business if far different from the TTRPG market and physical presence doe matter, people are going to go to a location that is close while books for any game can be ordered online. The total number of locations of McDonalds compared to all other fast food restaurants? They have 14% of the stores (
2). In other words, in no way shape or form do they dominate the fast food industry, they just happen to be the biggest single restaurant out of the top dozen chains.
In order to be as dominant in the TTRPG market, you have to have something other than just advertising and name recognition. If that was all that was necessary, there is no reason for previous versions to see an initial burst of sales and then fall off after a short period of time.