You know, I kinda think you are. Particularly since your own link doesn’t support the definition you’re using. A hack is not merely a professional writer. That’s a ridiculous debasement of the term. Under that definition, the only way for a writer not to be a hack is to either be a member of the idle rich, or be unpublished.
Rather, a hack is someone who has no investment in their own work. Their writing is purely a product to them, on which they place no more emotional importance than a Starbucks employee places on the frappacino they just poured. George Lucas is manifestly not a hack. He may not be a good writer - hell, he could be the worst writer since they invented the alphabet. But he’s clearly deeply invested in the world he’s created, often enough, to the detriment of his films. Similarly, while Shakespeare often wrote on commission, with more interest in pleasing some lord’s ego than in creating a personal expression, it would be very difficult indeed to argue that, say, Hamlet does carry a tremendous emotional payment in its creation, being, as it is, named after his dead son. I’m less well versed in the history of E.A. Poe, but I’ve always had the sense from his works that he was somewhat desperate for approval, and his writing was the only way he say to achieve that. Again, he was often a commercial writer, and at times a popular writer, but I think he derived a great deal of his self-esteem from his ability to write, which differentiates him sharply from a hack.
As to the question you raised latterly, about why we forgive the suckiness of the original trilogy, and not the prequels, I’d say that the most obvious reason is that the original trilogy didn’t suck. Many of Lucas’s deficits as a writer are obvious in Star Wars, but the film works because the younger Lucas, perhaps being more aware of his own limitations, created a story that did not rely on strong characterization and emotional depth. It’s an entirely plot-driven story, populated by characters that are drawn in broad strokes, whose motivations do not require terribly subtle acting to convey. The prequels, to the contrary, are character driven, and that, more than anything else, is where Lucas steps in it, because he cannot do characterization. The central arc of the prequels is the internal conflict of Anakin Skywalker, and that sort of story requires a subtle character touch that Lucas has never possessed. He’s never able to create in Anakin a character that anyone can care about one way or the other, and so the entire story fails, because it’s central conflict is entirely uninvolving.