Bruno Senna drove for HRT in 2010 and spent most of 2011 as a reserve for Renault. Photo: Getty
While Button went on to win the world title for the reconstituted Brawn team in 2009, Senna was left to scrape around for a drive in sportscars, biding his time before another chance in F1 came up, before landing a drive with the nascent HRT outfit in 2010.
The dream turned into a nightmare as the team limped through their maiden season, and for Senna it was a relief to leave, even if it again meant he did not have a full-time grand prix drive.
He spent most of 2011 as a reserve driver for Renault, doing very little driving, before being drafted in to replace the sacked veteran Nick Heidfeld for the final eight races of the year.
The fractured nature of his brief F1 career so far reflects that of his rise up the junior formulae and means it is very difficult to assess the quality of a driver on whom, realistically, a post-restructure Williams will depend to revive their failing fortunes, given the erratic form shown by his team-mate Pastor Maldonado in his debut season last year.
Senna's path to the Williams seat was eased by a substantial sponsorship package from Brazil, a situation that will inevitably see him labelled in some quarters as a 'pay-driver'.
This is quite a stigma in F1 - it traditionally means the driver needed to bring money to make him attractive to team, the implication being that his talent on its own was not enough.
Both he and Williams were at pains to emphasise on Tuesday that they had put their new driver through a rigorous assessment programme before signing him up - and that any talk of money had followed only once they had established to their satisfaction that he was good enough.
"We had an extensive driver-evaluation programme with a handful of drivers," said chief engineer Mark Gillan, "and we made the final decision based on raw pace, consistency, tyre management, technical feedback and mental capacity - and most importantly the potential impact they would have on the team.
"In all those areas it was very clear that Bruno has not had a lot of experience in single-seater racing, but has consistently shown improvement and real talent."
Of course, Gillan would say that - Williams chief executive Adam Parr spent a long time last year trying to convince the world that Maldonado was not a 'pay-driver', despite the sponsorship deal with Venezeula's national oil company that accompanied him to the team.
Maldonado has talent - he out-qualified team-mate Barrichello at Monaco last year, for example - but it is fair to say that he would not be in an F1 car without that help.
Senna is a different case.
Ayrton Senna once said of Bruno: "If you think I'm good, wait until you see my nephew." That, though, was when Bruno was cutting his teeth in karts in Brazil as a child. The great man's death brought Bruno's fledgling career to a shuddering halt at the age of 10.
His family forbade him from racing, and it was not until 10 years later - very late for a man to start a career in single-seater racing cars - that Bruno was able to take it up again.
It has meant a career on fast-forward, and the necessity to soak up vast amounts of information and experience much quicker than his rivals.
Ayrton Senna once said of Bruno: "If you think I'm good, wait until you see my nephew." Photo: AP
Inevitably, that has led to mistakes, but there have also been flashes of real talent, even if it has remained difficult to form a conclusive judgement.
At HRT, the car was awful, the team struggling just to survive and his team-mate Karun Chandhok was then an unknown quantity.
At Renault last year, the qualifying scores between Senna and team-mate Vitaly Petrov - who had not only been in the car all year, but was also in his second season in F1 - were four apiece.
But of the four races where Senna was on top, two of them were the Belgian and Japanese Grands Prix, held at Spa-Francorchamps and Suzuka, two of the three toughest tests for a driver in the world, the other being Monaco. At Spa, on his debut for the team, Senna qualified a brilliant seventh, directly in front of double world champion Fernando Alonso's Ferrari, no less.
With a young driver, especially an inexperienced one, the key is always to look for the highs. The bad points, the crashes, the occasional clumsiness, can be ironed out. But without inherent pace, a driver is going nowhere.
They know a decent driver when they see one at Renault, who have been renamed Lotus for 2012. Trackside operations director Alan Permane has worked with Michael Schumacher, Fernando Alonso and Robert Kubica and he says his impressions of Senna were largely positive.
"I don't think there's any doubt about his pace," Permane says. "What lets him down - and he knows it - is his consistency. But he didn't get a chance to show it. He had eight races with us but a lot of them were compromised by car problems."
Permane admits that it is difficult to be sure exactly how quick Senna is because Petrov is not exactly a proven top-level benchmark.
"Bruno was at least as quick as - if not quicker than - Vitaly," Permane says. "It's difficult to say whether he's going to be an Alonso/Kubica/Schumacher character, but some drivers take a long time to come along.
"Look at Jenson Button - when he drove for us, Giancarlo Fisichella destroyed him, and Fisi would be the first guy to admit he's not a mega. He was a very good number two. But now Jenson's fantastic. Can Senna do that? Only time will tell.
"He's very confident, very relaxed, almost performs better under pressure. The cars these days are trickier to drive (than they used to be) for someone who jumps in cold. And I think he did a brilliant job to do that.
"There's definitely something there. He definitely can be there on merit."
Backed by a budget or not, then, Senna more than deserves a chance to show what he can do.
Source : http://www.bbc.co.uk/blogs/andrewbenson/2012/01/how_good_is_bruno_senna.html