Artistic Maturity = Artistic Conservatism = Lack of Creativity = No.
It's a simple fact of life, creativity lessens with age.
There is an inherent rawness, a magic if you will, that accompanies an artist in his first few steps, that will never be with him again as he matures in his technical prowess. As a result the only answer to this poll is a no.
Doing different things does not equal creativity. It can help find creativity, yes, but it is not creativity.
He's stuck in his ways, as it happens with old age. If you doubt it listen to his three BEST scores of this decade...
Harry Potter and The Sorcerer's Stone
Memoirs of a Geisha
Harry Potter and the Prisoner of Azkaban
Those were the only three where Williams stepped outside of the Lucas/Spielberg sphere of influence (Geisha = barely so). And of those three, the best one came from Alfonso Cuaron, who was never satisfied, who never said "just do what you do Johnny," who kept pushing John Williams to create something truly different that also carried the message of the film. It also drove John away from the Harry Potter series, but that's a different story.
In everything else we see him going through the numbers, spouting regurgitated materials with more flourishes and ornamentation. But there is really nothing that differentiates his scores of late.
For instance what differentiates the set piece of Indy 4, "Jungle Chase," from anything out of the Star Wars prequels? There is nothing inherently JUNGLE about it, for all I know it is accompanying the Battle Over Coruscant, or a duel between Obi-Wan and Anakin.
Compare that to "The Desert Chase" it FEELS like a desert, it is lonely it builds upon itself, it contains a narrative that is inseperable from the Desert Chase. Listen to The Mine Cart Chase....it sounds like a roller coaster.
I can sum up the difference in creativity between the two time periods right here:
The Desert Chase is desert chase music. Jungle Chase is chase music.
Oh come on Jessie, you know the Joker's siren is 10 times more readily remembered than the dooo-doooo-dooooo....something something Crystal Skull theme!
Hans Zimmer has no difficulty coming up with stick-in-your head melodies and themes. His problem is he can't develop them to save his life. He is generally also under the impression that music has to be melodic and completely tonal and pleasant in order to be memorable. Bernard Hermann is thrashing about in his grave.
On the flip-side, John Williams used to consistently pump out great themes and be able to sophisticatedly handle them, now he just throws a plethora of notes at the problem and hopes it'll solve it.
He's sort of stagnating in the same way Goldsmith stagnated in his late career, and yet very differently. They both have sort of lost their heart and spark, but Jerry resorted to ultra-annoying simplicity, while Johnny has fallen back on ultra-annoying spray painting his notes on paper.
Incidentally, they were both each others favorite living composers, so maybe one saw the flaw in the other and decided to rectify it.
I finally purchased Hancock...and WOW. John Powell still has to work on consistency, but this soundtrack is sort of what I mean by heart and spark. There's something exciting there, and you can feel Powell was excited to tackle the idea of a hobo superhero.
And that's the thing, when you stop being able to hear a composer's excitement for his task at hand, you know he's aged a bit. It's the point where the artist's art has stopped being his life and has become his artistic endeavor. And honestly, I can imagine why. Grandkids + Family Neglected in 40 years of scoring non-stop > Art. Any day. John's earned it, and the fact that he can still write what he is writing is impressive to say the least, despite what we may be saying.
I still hold that much of his 2000s film works outside of Harry Potter and Geisha were significantly weaker than he's ever been.
But Tintin and War Horse (War Horse especially) have made me eat my own words. The Maestro, by luck, or by sheer skill and talent has still got it.
I genuinely believe that if my assessment that the maestro had run out of steam was true, he would not have been able to give us the two scores he has this year. I hear excitement and energy from him. With Tintin, yes I still hear the flurry of notes, but on the whole most notes seem to be there with purpose, something I think has been lacking in the past. War Horse on the other hand just outright proves my "all he does...spray paint notes" comment utterly wrong. It's a score where I cannot find a note out of place...where I cannot find a moment with too little or too much. It's just right, from beginning to end. From the emotional to the comedy to the action, it is supreme.
It's perhaps too soon for me to label it (War Horse) as one of the top scores from the maestro just yet, we still haven't seen the movie. But suffice it to say....
I am pleased to have been proven wrong!