I think the one thing he’s “wrong” about, is that ROTJ codified anything about the setting’s potential.
Years of EU material - engagement from fans as writers just like he was at 15 - have taken the property in the diverse directions he craved throughout books, games, comics, etc. Stuff like the prequels’ commitment to slapstick, and the ST’s derivate nature is definitely symptomatic of ROTJ - but Star Wars as a whole is such a canvas, and in part because of its mythological nature. It has one of the most recognizable pop culture iconographies ever created.
What that does - the value of that, that a new IP doesn’t have - is that “The Galactic Empire” and “The Rebel Alliance” or “The Jedi” are a language unto itself. You can be literate - fluent - in Star Wars, and in broad ways too. Look no further than Tony Gilroy treating Star Wars lore as a history to research for Andor. George Lucas himself is able to make commentary on our assumed institutions by playing on the expectations of the myths he established.
These are the kinds of complex iterations that a blank slate story needs time and goodwill to build up to - not to mention on a meta level, wouldn’t have the cultural cache that the Star Wars iconography brings with it. There is genuine power - in a similar way a Christian could call something “demonic” and that has meaning - to Lucas making an observation about the world, and making it a contributing factor in the fabled, evil Galactic Empire’s rise. That’s allegorical weight that the Hunger Games’ Panem doesn’t have. That Dune needs to explain over two movies or more.
Star Wars is broad and pulpy, and that allows for depth in the margins, in iteration. It more than other sci-fi, is at the point of Sherlock Holmes: make him a doctor for this one, or Watson is Lucy Liu in this one, this one’s about his cousin, and here’s a heady deconstruction of his tropes. But it’s Star Wars, and it’s already a pastiche, ripe for modulation and dissection.
Not to say that narratives more blatantly about, say, the Troubles of Northern Ireland, police corruption in Baltimore, or the Bush administration - can’t also be great, but they have a different type of less palatable baggage; are limited by the scope of reality. Star Wars as a framework can go further off the tip, in those directions, far better than other sci/fantasy settings can. Especially because I think it’s encouraged by the original creator’s work (prequels) itself, more than maybe LOTR in a similar position ever would. Really the property is as dogmatic as its fanbase allows it to be.