Windows was, and continues to be, the market leader for the consumer computer market because there are very few alternatives and most of them suck for what the people want. Do you remember the operating system for personal computers that IBM released? No? You don't remember it because it was terrible. I can't even remember the name. There are some alternatives (e.g. Linux), but other than MacOS none of them have ever been particularly popular because their biggest selling point is that they aren't windows. Meanwhile, despite multiple attempts, Microsoft hasn't been able to extend their consumer product outside of PCs. On the server side, Windows Server is competitive but Linux is the most popular by a significant amount. Popularity in a competitive environment does mean that the product is good enough.
In the TTRPG market there's even less reason for one game's dominance because there's less interdependence with other products (software for PCs) where we care about compatibility. Nobody is arguing that popularity means the design is "definitely and inarguably right", whatever that means. But D&D is an entertainment product, in a market with other products that hit approximately the same price points, difficulty and target market. If D&D weren't good enough entertainment for people, it wouldn't maintain it's market dominance and continued to grow year after year.
So yes, I believe that in competitive markets with plenty of options popularity, and just as importantly growth in popularity year after year is an indication of adequate quality. Bestest quality evar? No. I like the game and it works better for me than other games I've looked into, played one shots in or read about. But I, and dozens of people I've played with over the years, like the game.
It's my favorite version of the game and I've never found another game I prefer so for me it is a high quality product even if it is far from perfect. For others, based on the popularity and year after year double digit growth? Calling D&D "adequate quality" is not exactly singing it's praises from the rooftops.