Compare and contrast two screen deaths. In Quentin Tarantino’s second film, Pulp Fiction in 1994, John Travolta’s Vincent Vega accidentally shoots Marvin, a minor character, in the face. The killing happens mid-sentence, in the blink of an eye; in the process Vince covers himself and his acolyte Jules in blood and guts. The scene is played for laughs and succeeds: the horror and suddenness of the event coax an appalled hilarity from viewers, exacerbated by the two hitmen’s reaction, which is to bicker about mundane practicalities.

In Once Upon a Time in Hollywood, Manson family member Susan Atkins, who slaughtered Sharon Tate and two others with her accomplices in 1969, is killed in self-defence by Cliff Booth (Brad Pitt) and Rick Dalton (Leonardo DiCaprio), by being beaten in the face with a tin can, savaged by a dog and torched with a flamethrower. The scene is also played for comic effect, but in a diametrically opposite way, since the intended humour derives from how prolonged and over the top the brutality is. The violence, though stomach-churning, plays out on a surreal sort of Tex Avery level.

The difference between the scenes tells the story of Tarantino’s career. In Pulp Fiction, the deaths are practically meaningless, at the service of a giddy postmodernism that delights in stylistic flourishes, wisecracking and the trappings of genre. In Once Upon a Time in Hollywood, the deaths of Atkins and her accomplices could scarcely be freighted with more meaning, since Tarantino is giving himself artistic licence to rewrite history by saving Tate from her death at the gang’s hands that night.

Tarantino’s filmography reveals a director in search of increasingly gruesome settings to validate his revenge fantasies and confer legitimacy on his blood-thirst. Revenge has been the motor of the director’s career, present from Reservoir Dogs through to Django Unchained, via Jackie Brown and Kill Bill. In Pulp Fiction, for instance, you find the theme in the character of Marsellus, whose brutal rape by Zed affords him the moral right to shoot his attacker in the groin and vow to torture him to death. Subsequent films found him looking to the past for narrative frameworks on which to pin the revenge he had always enjoyed.

For who could possibly find fault with mutilating Nazis, in Inglourious Basterds? What wrong might there be in bloody retribution against torturous slave owners, in Django Unchained? Bonus: Tarantino found, in his new role as the questing musketeer of history, that he could depict torture at squirm-inducing length (for instance when Walton Goggins’s character strips and tortures Django), as well as the gory and by now entirely justified revenge that this demanded.

Once Upon a Time in Hollywood finds Tarantino revisiting this trope, by again having fictional characters off real-life people, in this case Susan Atkins, Tex Watson and Patricia Krenwinkel. (Watson and Krenwinkel are in prison and Atkins died in jail in 2009.) It seems obvious that the act of revenge upon Atkins et al isn’t Cliff Booth’s or Rick Dalton’s – these schmoes don’t know who the Manson family are, or that the murders would be commonly interpreted as ushering in the end of the summer of 69, and with it the glory days of the old Hollywood that Tarantino celebrates in his film. The person taking his revenge here is Tarantino.

What was once a troubling facet in a body of work with undeniable verve and accomplishment, has now calcified in Tarantino’s work. The director appears stuck in a sort of arrested development, endlessly inventing new “far-out” deaths with which to entertain himself and his fanboys. How else to explain the outlandlish, cartoonish and juvenile violence in Once Upon a Time in Hollywood? The deaths in the film make ample use of comedic call-backs (to an earlier scene of the dog biting a bone and one of Rick firing flames), making clear that Tarantino is in search of guffaws here. In the film’s coda, the deaths are even laughed about by Rick and Jay Sebring (Emile Hirsch), who in reality died on Cielo Drive that night but in the film gets to joke about flamethrowers with Rick.

This violence might not be so tiresome if it wasn’t detrimental to Tarantino’s work. Tedious scenes of fighting in the first half of Once Upon a Time in Hollywood, designed to prefigure that ending, come at the expense of fleshing out the character of Sharon Tate. For a film intent on saving her from the destiny she met, this is a fault. The film’s fond evocation of an old Hollywood, likewise, is steamrollered by the immaturity of the grisly finale. And the teenager-ish violence that Tarantino indulges in sees him double down on his misogyny, which was perhaps previously less overt and which severely impedes the film.

Tarantino’s films are not concerned with any sort of etiology of violence. In fact, his puerile eye-for-an-eye scenarios hinder the sort of responsible classification of orders of violence that is called for when revisiting traumatic historical events. It is morally repellent to depict drugged and brainwashed cult members being slaughtered by a character who, we are told almost as an aside, murdered his wife – and it’s rancid to stage these killings as entertainment. The best course of action, if things really have to stay this way, would be for Tarantino to make a good, honest, completely brainless shoot-’em-up without any delusions of having something to say.

• This article was amended on 23 August. The original had three mentions of the character Cliff which should have been Rick. This has been corrected.