Terrific review - exactly what I thought of this horrid book. There's a bizarre school of thought that history is "boring" so you have to throw in loads of weird sex and ridiculous anachronisms to make it "interesting."
There's no doubt Gregory has it in for Anne: in interviews, the Q&A at the end of the book, and on her own readers' forum, she constantly states AS FACT that Anne "was a very bad person who never let sin or crime stand in her way - she was clearly guilty of at least one murder." On the other hand, her Mary Sue Boleyn is a "heroine." Now we have these pop culture characterisations perpetuating themselves in scholarship - there is one biography of Mary Boleyn already (Josephine Wilkinson - a few pages of facts and a whole lot of filler) which buys into the "Henry VIII's favourite mistress" nonsense (personally, I think his "favourite mistress" would have been Elizabeth Blount, who was the mother of his only son at that stage) and one on its way (courtesy of Alison Weir). On the other hand, countless online discussions, book reviews and blog posts - even those by history students! - have poor Anne described as "selling her sister down the river", "stealing poor Mary's son," "going after her sister's seconds" (which she didn't) and being the most evil scheming schemer from Schemerville in all of Schemedonia (which she wasn't). People even argue that she "could have" slept with her brother, who "could have" been bisexual - "well it's MY OPINION and you can't prove they didn't and he wasn't!" - even though there's not a shred of evidence of either, and if there's no evidence, that's it. Further a) even the Boleyn enemies didn't believe a word of the allegations, and they'd have been ready to believe the worst of Anne and her supporters; and b) if there was a shred of contemporary evidence that George Boleyn had male lovers, you can bet that his enemies would have got as much mileage out of it as possible - Chapuys would have gone into excruciating detail.
I totally agree with your view of George's characterisation here - he is the stereotypical "anything-sexual," something that not only betrays Gregory's lack of knowledge of the period and the personalities (if the real George had been attracted to Weston or Smeaton or whoever, he wouldn't have been so upfront about it - given his strong religious views, if he had fallen for another man, it would no doubt have caused him a great deal of anguish) but a lack of understanding of the complexity of human sexuality and an arguably homophobic bias. The notion Gregory seems to promulgate here, that a man who falls in love with another man (mind you, we're told this, but are never shown it - a constant problem throughout this book) is by definition deviant enough to be sexually attracted to his own sister and act on it, is highly offensive. I'm surprised - although relieved - she didn't make him a paedophile as well, maybe abusing a a ten or eleven year old Mark Smeaton when he first came to court *gag*. It's interesting that Gregory's "good characters" (Henry, Mary B etc) are as straight as they come. That said, I wouldn't be against a novel that did explore the possibility, provided it was respectfully done and didn't resort to cliché.
Despite this, the "IT'S FICTION!!!" brigade seem to be completely oblivious to why it's important to make an effort to get the HISTORICAL part of the FICTION right as much as possible. Even if you manipulate events for the drama, an author should at least try to recreate the period. Also, it makes for a better story - much of Henry VIII's marital sagas you couldn't make up.
Apologies for the long comment - I realise I'm preaching to the converted here!