As a pretty eclectic player interested in trying and playing all sorts of systems, I do think D&D (especially 5.0e--RIP) has a certain magic to it.
The rules have some rough edges, but the relative efficiency provided by the interaction of complexity with design goal is pretty high. In other words, if you like the level of complexity, the 5.0e D&D provides its intended experience efficiently. If you prefer more (or less) complexity, or you don't like the intended experience (like my friend who hates how much he feels they nerfed casters), or you just don't like class/level systems (like me, despite my liking 5e), you may not care for it, but other than some rough edges I think that is more about preference than quality.
D&D IP is also distinctive, expansive, and to me--wondrous. The reason I had a hard time staying away from D&D permanently when I gave up over the (actually) clumsy system back in 2e, is because of the Quasi-elemental Plane of Lightning, the City of Brass, the triad of Forgotten Realms, Greyhawk, and Dragonlance, the Phlogiston, 3rd level spells, beholders and displacer beasts. No one has/had all of that, because it's real IP, and I love it as much as any Star Wars expanded universe or Marvel fan.
I agree with the original premise that it's not good for the market (or for D&D!) for it to have such a stranglehold on the industry. I agree that some of major reasons for its popularity are unrelated to its quality. I do not agree that its popularity is in spite of low quality.