The safest place to be at a modern grand prix meeting, Martin Brundle said the other day, is in the cockpit of a Formula One car. Since that dreadful weekend almost 20 years ago when Ayrton Senna and Roland Ratzenberger died at Imola, the world's best drivers have made a habit of emerging more or less unscathed from the most bloodcurdling accidents.

Brundle was appearing at the London Film Festival, introducing a new documentary about the history of the world championship. Titled 1, it tells the story, he said, of "how it became unacceptable to die in the name of sport". Of how Formula One changed its nature, in other words, to the extent that as Sebastian Vettel hurtles towards a fourth consecutive world championship in India this weekend, the question of his personal safety is more or less removed from the minds of his fans.

Things were different for his predecessors – and for those who watched them at work. The film contains a scene in the pits at Watkins Glen during practice for the 1973 US Grand Prix, showing Colin Chapman, the boss of Lotus, and Peter Warr, his team manager, reacting to the news of a big crash.

"Who is it?" Chapman asks.

Warr tells him it's François Cevert, the Tyrrell driver.

"How bad is he?"

"Very bad."

"Cevert. Bloody hell."

Twenty-four hours later Chapman is leaping in the air on the finish line to celebrate a victory for his driver, Ronnie Peterson. That's how it was in those days, just as it had been at Monza in 1933 when three top drivers died in a single day or at Le Mans in 1955 when 82 spectators were killed in front of the main grandstand. The race went on.

No man did more to change attitudes than Jackie Stewart, Cevert's team-mate and mentor, who responded to his protege's death by declining to race in what would have been his 100th and last grand prix, ending a career in which he campaigned for the use of seat belts, flameproof overalls, safer circuits and proper medical facilities.

Cevert's accident was also the reason Roman Polanski lost interest in Formula One. The film director had been a close friend of Stewart and in 1971 they collaborated on a remarkable film called Weekend of a Champion, which has now been restored by Mark Stewart, Jackie's film-making son, and was also screened at the festival. In a new epilogue the protagonists return to Monaco, the scene of the film, to ruminate on what it all meant and how things have changed.

They review old footage of fatal accidents alongside recent spectacular crashes. "Sometimes it's like cinema special effects," Polanski says, while watching Mark Webber's car somersault at close to 200mph in Valencia a couple of years ago, landing upside down before careering into the barriers. "Then the guy just gets out and walks away."

Stewart remembers rushing to the scene of Cevert's accident, where the Frenchman was lying dead from massive injuries in his mangled car. "What I saw that day," he says, "no man should ever see." He mentions that five of his closest friends were killed during his eight years in Formula One: it was to his wife, Helen, that the task of comforting their wives and girlfriends fell, as well as that of helping them pack up the dead men's belongings.

Spectators, he agrees, still want a sense of danger. "They want to see violence – because when a racing car goes off the road it's a tremendously violent thing." The improvements in safety over the past 40 years, he says, represent "a risk-management victory".

So that is just one of the ways in which the debate over Vettel's precise standing in the ranks of the all-time driving greats can never be resolved. Although Vettel undeniably needs courage to do what he does, it is a different order of courage from the one required in the 1950s by Juan Manuel Fangio, the first of the six world champions to whom Christian Horner, Vettel's team manager, compared his driver this week.

But then Fangio didn't have to cope with a steering wheel full of buttons and dials, with the critical nature of modern tyres, with technology that cuts half the engine's cylinders during a corner, with Kers and DRS, with 20 races a year rather than eight or nine or with instructions from a race engineer filling his ears in the heat of battle. Vettel also has to handle the constant scrutiny to which modern celebrities are subjected, identifying and magnifying the slightest behavioural flaw.

Yet, still we insist on making comparisons. Jim Clark, Stewart, Senna, Alain Prost and Michael Schumacher were the other five mentioned by Horner and although a comparison of statistics is always a problem when parallels are drawn between achievements in the same field of sport across very different eras, in this instance there is one figure that is impossible to argue with: the ratio of wins to races.

Measuring Horner's half-dozen by that yardstick, we find Fangio in the lead, having won 47% of his races (24 from 51), followed by Clark with 34% (25 from 72), Schumacher with 29% (91 from 306), Stewart with 27% (27 from 99), and Prost, with 25.8% (51 from 198) – just edging out his great rival Senna's 25.5% (41 from 161). The one Horner forgot was Alberto Ascari, the first double champion in 1952-53: the Italian's 13 wins from 32 races, give him 40%, bettered only by Fangio.

And where does that put Vettel? His 35 wins from 116 races represent a 30% average, ahead of everyone except Fangio, Ascari and Clark. That is the one figure that tells us how good he really is.

Attempts to devalue his achievement by pointing out that he has the best car are beside the point. All the great champions made it a priority to have the best equipment at their disposal. It is what Vettel does with it that makes the difference. And he won his first grand prix five years ago, not in a Red Bull but in a Toro Rosso, at Monza in the rain, aged 21.

Maybe, as Anthony Davidson suggested in these pages the other day, today's circuits are so neutered that poor driving is no longer even mildly penalised. But only a fool would take Vettel's good luck to be racing in an era made relatively risk-free by the work of Stewart and others as proof that he would not have distinguished himself at any time in the sport's history.

• This article has been amended to correct Sebastian Vettel's position from third to fourth in the wins to races list