They were - or at least started out as - the ugly ducklings of the sportscar world. They forsook 20 or 30 years of technological advancements in motorsport. And they weren't as quick as what had gone before.

Daytona Prototypes had the odds stacked against them in our European eyes, but is it time to reinterpret the place in history of a class that bowed out earlier this month at the Petit Le Mans enduro at Road Atlanta?

Should the category, created for the NASCAR-owning France family's Grand-Am series in 2003, be dismissed just because a Crawford, Riley, FABCAR or Doran DP wasn't an Audi R8 LMP1 car? Nor that they weren't an MG-Lola EX257, the car that on occasion used to beat the German metronome in the rival American Le Mans Series in the years during which the DP class was establishing itself?

That's not the point. A DP wasn't trying to be an LMP1 car, not even a poor man's version of it. The category was something different altogether and needs to be judged on its own merits.

The class was a reaction to Le Mans-rules prototypes rather than some kind of North American copy. The formula was conceived so that indigenous constructors could make cars at a time when the LMP cars on the ALMS grid were for the most part produced in Europe. Even the front-engined Panoz roadsters that took the fight to Audi in 1999-2002 were designed and largely built in the UK.

And it was devised to be cost-effective and accessible because most teams in North America couldn't afford to buy and run an Audi, even if they could get their hands on one. The DP category was inclusive in its philosophy. The idea was that the same specification of car would be available to all, and if your team and drivers were up to the job, you could be competitive.

Grand-Am's hierarchy ignored the latest carbon-composite technology when framing the rules for the 2003 season. DPs employed NASCAR technology and were built around panelled spaceframes, or tubeframes in American parlance. Steel brakes were mandated and there was no paddle-shift gear change.

The cars were cheap to buy in comparison to the carbon counterparts on the other side of the sportscar divide - a Riley MkXI rolling chassis cost $375,000 or barely over £200,000 in 2004 - but more importantly they weren't expensive to run.

They were big burly bruisers of a racecar.

"We overspecced a lot of the components. They were bigger and heavier than they needed to be," says Mark Raffauf, who helped write the rules and is now a big cheese within the IMSA sanctioning body post-merger. "One of Ganassi's cars had over 40,000 miles of competition just at the Daytona 24 Hours. We over-engineered everything."

And no end-date was set for the rules. Grand-Am's first boss, Roger Edmondson, once said that DPs would race for 20 years. He wasn't far wrong.

"I was a driver at Daytona in 2002 when they announced the DP class and the tagline I remember was 'prototype racing for the cost of GT racing'," recalls Peter Baron, whose SAMAX and Starworks teams both enjoyed success in the DP ranks. "I was among the naysayers initially, but Grand-Am got it right.

"In my first year as a car owner in 2006, we did 15 races for a budget of $1.8million. That was good value, and we knew that the cars were never scheduled for obsolescence.

"We didn't have that three-year rules cycle, and then everything is worthless and you've got to spend another million dollars to tool up again. As a business model, it was fantastic."

The team owners who flocked to Grand-Am, the likes of Baron, Michael Shank with his eponymous squad and Bob Stallings under the GAINSCO banner, did so in the knowledge that they could be competitive.

"I couldn't afford to buy a P1 or P2 car and go and do the ALMS, but I could afford a DP," says Michael Shank, whose team graduated from the Toyota Atlantic ranks and ended up winning the Grand-Am blue riband at Daytona in 2012. "I could buy the same stuff that Chip Ganassi could buy."

Indeed Oswaldo Negri Jr put the Michael Shank Racing Riley-Lexus on pole on its debut at Laguna Seca in 2005, admittedly after the team had undertaken a part season with a Doran the previous year.

"The beauty of the DP formula was that you could buy a car, and if you ran a good team and had a good driver, you could immediately run at the front," says Bill Riley, whose eponymous organisation built more DPs than anyone else.

Riley recounts a story about one of his cars that gives an insight into both the success of the category and his Riley Technologies concern. The MkXI designed by his father Bob didn't race until the second season of the DP formula for the simple reason that he was unable to sell any in 2003.

Chip Ganassi Racing and Wayne Taylor bought cars for the following year, but it was the performances of smaller teams with Riley machinery that proved decisive.

"I sold a car to a guy called Paul Mears Jr, and Sylvain Tremblay ran the car at SpeedSource and was his co-driver," says Riley.

"We were at Daytona for the July race and Wayne was in our car [Riley ran the car under the SunTrust Racing banner] and Scott Pruett was in the Ganassi car. Sylvain went past the both of them, and it was his first race with the car.

"I knew Sylvain was a pretty good driver, but no one else did. The field saw a guy buy a car, show up and lead the race."

That was just as important in boosting sales of the Riley as Ganassi's successes, he insists. Riley Technologies would go on to build nearly 50 DPs having failed to sell a single one in the first year of the formula after a disastrous foray into IndyCar racing.

An interesting aside is the link with Ganassi, whose purchase of cars for the 2004 season helped save a company that Riley says was "getting ready to shut down". The relationship between Ganassi and the Riley family dated back to the late 1970s when team boss Chip Ganassi had once driven the Protofab Super Vee designed by Bob at Watkins Glen.

Business boomed for Riley Tech, but it also did for Grand-Am. The DP class flourished in the middle years of noughties. There were 30 of the things on the grid at the Daytona season opener in 2006, a record that was nearly matched the seasons either side. There were 29 DPs in 2005 and 28 in 2007.

Perhaps more importantly, the entries held up away from the prestigious enduro at the start of the season. Average car counts were nudging 25 in the glory years.

Those massed grids certainly made for a spectacle. The racing was close, very close. "It was, in its heyday, badass hardcore racing," says Baron.

But then the cars were designed to create good racing.

The low-downforce cars could run nose to tail. Steel rather than carbon brakes and control tyres, combined with the lack of aero and a hefty minimum weight, meant long braking distances.

"They were big cars to stop," recalls double Grand-Am champion Max Angelelli. "Everything happened in slow motion. That meant you could make a mistake and get away with it, but it also made for great racing."

Nudging and nerfing was part of the scene, and that too came from the way the cars were built.

"Those cars could take a hit," recalls Scott Pruett, a five-time Grand-Am champion with Ganassi and the most successful driver in the history of the class with 44 wins. "You might knock the toe out, change the camber or plain bend up the car, but you could still go racing and get after it. It was hard, brash, fender-to-fender racing."

That philosophy of the DP was irrevocably altered upon the merger between Grand-Am and the ALMS for 2014. The need to increase the performance of the cars in the face of opposition from LMP2 machinery sent costs spiralling and removed a degree of the 'raceability'. The rules stability on which so many teams had based their business case was also removed.

The DP was given a further two seasons from 2014 and then a third, so that's now it for this tubeframe throwback. The cars might have offended our European sensibilities, but the category achieved its goals.

Walk up and down the pitlane at next year's IMSA SportsCar Championship opener at Daytona, and you'll be certain to find team owners and drivers ready to sing the praises of the cars we hated on this side of the Pond.

"I owe everything to the DP; I built my business on that class," says Shank. "You'll never get me to say one bad word about the Daytona Prototype."