Prime ministers have called it “malicious nonsense” and “complete rubbish”. Theatrical dames have criticised it as “crude sensationalism”. And now the notices for the new season are in, they don’t make pretty reading, either. The Guardian’s Lucy Mangan found it so excruciating to watch whilst delivering her one-star verdict that she felt like she was having an “out-of-body experience”. Other critics have called it “clumsy and crass”, “ill-judged and outrageous”, “pointless and sad”, “a disappointing new low”, “a very pretty bore”. Let’s call them “mixed reviews”, shall we?

Somehow The Crown – that everyday story of blue-blooded folk – has become the most divisive drama on TV. Forget Euphoria’s druggy orgies or The Idol’s horrendous misogyny. The real shocker on our screens is a family of billionaire toffs gazing mournfully out of palace windows and clapping politely at polo matches.

The Crown’s controversy-bait status has been a gathering storm. When Peter Morgan’s regal saga first swept on to Netflix in 2016, it was lavishly produced and largely non-problematic. Most viewers had no memory of the postwar events it dramatised (the debut run covered 1947 to 1955 – like, totally olden times) nor strong views about them. The people it portrayed (Winston Churchill, Wallis Simpson) were long dead. Any arguments were limited to whether actors looked enough like their real-life counterparts. It was part posh soap opera, part history lesson. Emmys and Golden Globes were duly plundered like colonial treasures.

Over its six seasons, The Crown has steadily caught up with modern times and this has become a mounting problem. Suddenly most of its characters are alive, vocal and consulting their lawyers. Viewers now have vivid memories and their own takes. The closer The Crown creeps to the present, the more historical distance is lost and the more contentious it becomes.

There were early grumblings about speculative storylines, such as young Princess Margaret’s wish to be queen or Prince Philip’s refusal to kneel at his wife’s coronation. The real Philip considered suing Netflix over the “upsetting” season two subplot where he was blamed for the 1937 death of his sister, Princess Cecilie. The backlash had ramped up by the fourth season, described by the Guardian’s Simon Jenkins as “fake history … reality hijacked as propaganda and a cowardly abuse of artistic licence”. The royals themselves stayed characteristically tight-lipped but Charles’s biographer Jonathan Dimbleby called it “nonsense on stilts”.

There is an argument to say The Crown is merely a scapegoat, taking the rap for a wider shift in attitudes. Due to intrusive press coverage, oversharing interviews and soul-baring memoirs, we know more about the royals than ever. Is it Netflix displaying a lack of reverence or our entire contemporary culture? Does today’s scandal-prone monarchy merit reverence anyway?Morgan was called “callous” for using the death of five-year-old Leonora Knatchbull to precipitate an insinuated romance between her mother Penny and the Duke of Edinburgh. It was widely mocked as jarringly EastEnders-esque when Charles raged at his mother: “If we were an ordinary family and social services came to visit, they would have thrown us into care and you into jail.” Increasingly, The Crown’s imagined dialogue sounds like generic scriptwriting, rather than how these people might actually speak.

Nowadays coverage of the series is more about factchecking it than considering its merits as screen entertainment. Many critics seem confused by the difference between drama and documentary. How dare Morgan lightly spice up events to make them more compelling? Why invent dialogue for the royals and not base the whole thing around dignified silence? Let’s all march on Netflix, waving pitchforks and cuddly Paddington bears.

Unfortunately, the growing controversy coincided with the show’s quality falling off its throne. Biseasonal cast changes haven’t helped. The line of succession from Claire Foy to Olivia Colman to Imelda Staunton has delivered diminishing returns. Jonathan Pryce’s harrumphing incarnation of Prince Philip is a shadow of the nuanced figure portrayed by Matt Smith and Tobias Menzies.

Hard-partying Princess Margaret – an MVP in early seasons, when Vanessa Kirby was terrific and Helena Bonham Carter quietly heartbreaking – has been reduced to fleeting, fag-puffing cameos from a wasted Lesley Manville. Emma Corrin’s empathic embodiment of teen Lady Di propelled them to stardom and Elizabeth Debicki now shines but many remain unconvinced by Dominic West as Charles.

The final season drops in two parts – the first four episodes arrived this week, the last six follow on 14 December – and is dominated by Diana, Princess of Wales’s untimely death. Netflix has been at pains to point out that the 1997 Paris tragedy is depicted “delicately”, assuring pearl-clutching pundits that “the exact moment of crash impact won’t be shown”. Morgan told Variety: “Oh God, we were never going to show the crash. Never.”

Regardless, it is still being berated for poor taste and liberty-taking. The phrase “too soon” has been bandied about. So has the phrase “disaster porn” – before the episodes were seen, naturally. As Morgan said: “All the criticism comes in anticipation of the show coming out. The minute it’s out and people watch it, they instantly fall silent. And probably feel rather stupid.” He has a point but it’s wishful thinking on the “fall silent” part.

It was deeply risky depicting the Pont de l’Alma tunnel crash, which mercifully isn’t seen, only heard. Bafflingly, it’s framed by whimsical scenes of a whistling Parisian taking his dog for a moonlit walk. He’s pleading with the pooch to do its business when a Mercedes hurtles past, tyres squeal and a sickening crunch is audible. It’s a strange creative choice, to say the least.

Appearances of Diana’s ghost provide a further flashpoint, guaranteed to send Middle England swivel-eyed with outrage. Morgan has denied that her posthumous cameos, talking gnomically to Charles and the Queen from beyond the grave like a willowy Yoda, are strictly spectral. “I never imagined it as Diana’s ghost in the traditional sense,” he said. “It was her continuing to live vividly in the minds of those she left behind.” When she appears from beyond the grave, she genuinely announces herself with a camp “Ta-da!”

Still the clangers keep coming. Foreshadowing of Diana’s death is ham-fisted. Dodi Fayed’s ghost pops up, presumably as a gesture towards equal opportunities in the afterlife. While young Harry is gut-wrenchingly weepy about “Mummy’s” death, Prince William turns into Kevin the teenager – angstily stomping around Balmoral listening to Radiohead. The suite of episodes closes with a moment so silly it’s more likely to make viewers laugh than cry.

In the run-up to this week’s global release, Team Crown embarked on a preemptive “positive publicity drive” in a bid to calm the inevitable blowback. Morgan seemed tetchy and defensive in interviews. No wonder. It all feels an awfully long way from the show’s early highs: Foy’s gong-garlanded performance, the Kenyan tour, Aberfan, the Great Fog, the Marburg Files, those sumptuous $15m-per-episode production values.

What began as a prestige period piece now resembles a trashy telemovie. The untold historical stories and clever parallel plots of earlier series have fallen by the wayside. Slow-burn subtlety has been swapped for splashy melodrama. In seven years, The Crown has gone from a superior Downton Abbey to a gossipy guilty pleasure.

Yet despite all the fact v fiction hand-wringing, it still tops Netflix’s most-viewed charts. In its home stretch, however, this lightning-rod drama has royally lost the plot. We’ll still watch it but we won’t admire it: a sentence that might equally apply to our feelings about the House of Windsor itself.