Too good to be true protagonists

Why are so many protagonists in modern novels too good to be true? Is this a modern phenomenon? Is it particularly found among American novels, perhaps as an expression of the American dream?

Such protagonists are sometimes called a ‘Mary Sue’ or ‘Marty Stu’, defined by wikipedia as "a character archetype in fiction, usually a young woman, who is often portrayed as inexplicably competent across all domains, gifted with unique talents or powers, liked or respected by most other characters, unrealistically free of weaknesses, extremely attractive, innately virtuous, and/or generally lacking meaningful character flaws. Usually female and almost always the main character, a Mary Sue is often an author's idealized self-insertion, and may serve as a form of wish-fulfillment. Mary Sue stories are often written by adolescent authors. ... As a literary trope, the Mary Sue archetype is broadly associated with poor quality writing."

It's not a new phenomenon. In an essay written in 1856, George Eliot characterised what she called "Silly Novels by Lady Novelists" as having a heroine who "is usually an heiress, probably a peeress in her own right, with perhaps a vicious baronet, an amiable duke, and an irresistible younger son of a marquis as lovers in the foreground, a clergyman and a poet sighing for her in the middle distance, and a crowd of undefined adorers dimly indicated beyond. Her eyes and her wit are both dazzling; her nose and her morals are alike free from any tendency to irregularity; she has a superb contralto and a superb intellect; she is perfectly well dressed and perfectly religious; she dances like a sylph, and reads the Bible in the original tongues. Or it may be that the heroine is not an heiress—that rank and wealth are the only things in which she is deficient; but she infallibly gets into high society, she has the triumph of refusing many matches and securing the best, and she wears some family jewels or other as a sort of crown of righteousness at the end. Rakish men either bite their lips in impotent confusion at her repartees, or are touched to penitence by her reproofs, which, on appropriate occasions, rise to a lofty strain of rhetoric; indeed, there is a general propensity in her to make speeches, and to rhapsodize at some length when she retires to her bedroom. In her recorded conversations she is amazingly eloquent, and in her unrecorded conversations amazingly witty. She is understood to have a depth of insight that looks through and through the shallow theories of philosophers, and her superior instincts are a sort of dial by which men have only to set their clocks and watches, and all will go well. The men play a very subordinate part by her side. ... They see her at a ball, and they are dazzled; at a flower-show, and they are fascinated; on a riding excursion, and they are witched by her noble horsemanship; at church, and they are awed by the sweet solemnity of her demeanor. She is the ideal woman in feelings, faculties, and flounces. For all this she as often as not marries the wrong person to begin with, and she suffers terribly from the plots and intrigues of the vicious baronet; but even death has a soft place in his heart for such a paragon, and remedies all mistakes for her just at the right moment. The vicious baronet is sure to be killed in a duel, and the tedious husband dies in his bed requesting his wife, as a particular favor to him, to marry the man she loves best, and having already dispatched a note to the lover informing him of the comfortable arrangement. Before matters arrive at this desirable issue our feelings are tried by seeing the noble, lovely, and gifted heroine pass through many mauvais moments, but we have the satisfaction of knowing that her sorrows are wept into embroidered pocket-handkerchiefs, that her fainting form reclines on the very best upholstery, and that whatever vicissitudes she may undergo, from being dashed out of her carriage to having her head shaved in a fever, she comes out of them all with a complexion more blooming and locks more redundant than ever."

Precisely.

Recent books which I have found less than satisfying because of the presence of such characters include:

• A Little Life by Hanya Yanagahira in which the protagonist Jude is so clever that when he is employed as a private tutor it is to teach "Latin, math, German, and piano" (2.1). He is very handsome, cooks like a cordon bleu chef, is a brilliant gardener, and has a great singing voice. He becomes a hugely successful lawyer. He works incredibly long hours, often six days a week, sometimes staying at the office until sunrise. Nevertheless, he never seems to collapse for lack of sleep. He also fits in an active social life, attending plays, films, art gallery openings, and dinner parties galore. Furthermore, all of his friends are incredibly successful. Of the four penniless college buddies we encounter at the start of the book one becomes a major visual artist, one a respected architect and one a major film star (who nevertheless maintains artistic credibility). His extended friendship group is also full of high achievers. Where do they find the time for it all? I can only assume that the secret of their success is that they don’t have children, never watch TV and rarely read a book.
• The Judgement of Paris by Gore Vidal in which the hero, Philip, is rich, intelligent, cultured, and so good-looking that he is incessantly wooed by both men and women.
• The Keeper of Stories by Sally Page in which the protagonist Janice may be 'just' a cleaner, as her husband keeps reminding her, but she is an extraordinary cleaner and an extraordinary woman whose services are in high demand around Cambridge, UK. She cleans for an opera singer and an ex-spy, amongst others. Her neighbour used to play cricket for India, the shoe-shop assistant used to play squash for England. But then, Janice's own father was a university professor and the bus driver's dad ran a bookshop. It's quite a place, Cambridge!
• Black Cake by Charmaine Wilkerson in which Byron is "the African American social media darling of the ocean sciences" (he's also a "brainy athlete"), one of his mother's friends becomes a world-record holder for endurance swimming, and his half-sister is another social media and TV star, this time for cooking, who wipes the floor on live TV with a "coffee guru".
• A Gentleman in Moscow by Amor Towles in which the main character has a superb palate, is a fantastic marksman, charms everyone (except for the weaselly waiter who becomes the hotel manager), is such a sensational lover that a world-famous actress sleeps with him every time she comes to Moscow over a period of at least twenty years, is always perfectly groomed and dressed and is a perfect raconteur, full of amusing stories with wisdom at their heart. But then almost everyone else in this book is perfect, including the child he adopts who is naturally brilliantly talented at the piano.
• Lessons in Chemistry by Bonnie Garmus in which the lead character, Elizabeth and her daughter Mad, are hugely talented to the point of genius (as is their dog).
• Where the Crawdads Sing by Delia Owens in which the protagonist is a female version of Tarzan who learns to read in a few weeks and becomes a famous author.

You expect this sort of superhero in James Bond style thrillers such as The Malta Exchange by Steve Berry, The Four Just Men by Edgar Wallace. But thrillers are never meant to have believable characters. It seems these unbelievable characters are beginning to infect more serious fiction, fiction that some people associate with quality fiction.