Nothing that hasn't been said before. Not sure why it's being said again.
Yes, the film has a creakiness, obviously having been hampered by its budget and somewhat uninspired directing. But Wilder's performance is brilliant (no matter what Dahl thought), and that's what fans appreciate (along with the music, and everyone's secret wish for consequences for spoiled brats and their indulgent, irresponsible parents).
But Willy Wonka isn't sadistic, and it's wrong to describe him that way. None of what happens in book or film is either sought by him nor done by him— the children place themselves in danger by their own selfish choices and actions, and the parents are clearly presented as being irresponsible for not teaching their offspring how to be Good People. Willy Wonka merely allows their choices, made with free will, to bear the natural consequences— and then sends his friends and servants, the Oompa Loompas, to correct the children's mistakes and save them, though not without the lingering results the actions caused. Charlie, on the other hand, is kind and considerate and honest, admitting his own mistake and not succumbing to greed or selfishness— and for that, he receives the Keys to Heaven. It's a story about personal responsibility, integrity, and making the right choices, and the film does make this come through. (In some ways it could even be classified a religious allegory.)
But I agree that there's no point in remaking the film, much less this horrid concept of a "prequel." We're not supposed to know who Willy Wonka is or what his childhood was— he doesn't *have* a childhood, he *is* childhood trying to hold on to its innocence. And what is all that ridiculous blather about "capitalist"? Neither the book nor the film have anything to do with socioeconomics. Willy Wonka runs a chocolate factory because that's what the story requires. What does that Guardian writer want it to be— "Willy Wonka and the Organic Sugar-free Naturally Sourced Collective Co-op Commune?" It's a stupid shot made by the sort of idjit who doesn't realize that despite its professed political slant, The Guardian (and the writer himself) is capitalistic in all respects, existing to (gasp!) Make A Profit for its employees and investors. Perish the thought! Wonka is a factory owner because factory owners are a Real Life Thing, and being a factory owner isn't automatically a negative (quite the opposite) except to hypocritical twits, delusional fanatics, and misguided ignoramuses. But either way, it's irrelevant to the discussion of either the book or the film. Wonka could be a zoo owner, or the Gardener of the Most Awesome Garden in the World, or Walt Disney. He's simply the Man with the Key to Paradise. What that paradise is or how he came to be the Man in Charge is of no importance.
Dahl is best read for what he is, and the film is best enjoyed for what it is.