It's not at all unprofessional to disagree with a director, and in fact I would find it more unprofessional for a composer to act as a Yes-Man. And experience has little to do with it - before "Phantom Menace," Lucas had only directed American Graffiti, THX and A New Hope, and he had been out of practice in the directing world for 22 years (and it shows). Williams was infinitely more experienced than Lucas, and if Lucas had any sense he would have trusted Williams 100% of the way (which, for all we know, he did). If Lucas had insisted on that particular tone of the music to the point where Williams, had he disagreed, felt that he had better leave the project, well, that would have been professional of Williams as well. Of course we're talking entirely hypothetically here, who really knows what was going on. But there's a good argument to be made that the disaster that was "Phantom Menace" was entirely the result of George surrounding himself with Yes-Men - whether or not Williams was one, well, who knows. It's not really the point, the point is that a composer as famous and rich as Williams is 100% responsible for any music he writes in a film, no question, regardless of whose idea it was, unless the director I guess played tricks during the editing or the mixing. Given the standard to which Williams clearly holds himself to, I'm sure he would agree with me. At that level, a director may be the boss, but the composer is not his slave.
Anyway, you didn't really respond to anything I said - we're in agreement that "Duel of the Fates" is well made music, but you didn't address anything I brought up re: it being a pretty close replay of Orff, or more importantly the pretension of music that was made to encapsualte huge ideas being the score for a movie about space wizards.
As for the new things you brought up, it's true that what Williams wrote is very impressive for a 70 year old, and it's also true that it's less vital than Star Wars/Raiders/Close Encounters/Superman era Williams. If you want to pinpoint where the spark died down, I'd go way back actually. I don't even find that his 90s work (yes, even Schindler's List)