With the level of pay drivers and politics and regulations, I disagree. Why is Sergio Perez where he's at? Money. Why are Andre Lotterer and Loic Duval at? Because they're among the most talented racers in the world. Sportscar drivers drive hard and drive smart among conditions that would bring some F1 drivers to their wits end. Maybe if it was 2010 I would agree with you, but with Audi, Toyota, and Porsche among others going for Le Mans in 2014, it will be competitive as ever. If Mark got the WDC in 2010 people would just dismiss it as him having the car do the work, same as with Jenson. With him having the wins he does have in F1, Monaco, Silverstone, Nurburgring plus his record in sportscars should he pick up a Le Mans, he'd be right up there with Brabham as one of Australia's best ever and one of the best drivers to never win a WDC.
Alright lets break this down.
1. F1 now is no more littered with pay drivers than any point in the past. Check out the fields from the early 1990s where you had teams and drivers who never pre-qualified for a race, much less start one. Regardless we do not hold that against the greats such as Senna, Prost, and Mansell.
2. All racing requires money, some have more money to bring, others have less. To hold one series higher because they have a greater number of guys who couldn't get enough money lined up is silly.
3. Le Mans racing is chock full of drivers who are there just because they have enough money to do so. In fact they even have a class for it, LMGTE
AM.
4. People can very easily question if it was the car in Le Mans as they can in F1. For instance in 1991, the 787b was not the best car there the Silk Cut Jags were faster, but they ran into problems during the race. Or this year, Audi could have locked out the podium but they ran into mechanical issues. Does this reflect badly upon the driver or the car? Also with driving duties split among 3 drivers, aren't you only as strong as your weakest driver?
With that said, if Webber achieves success with Porsche it will certainly help his career. I also have the utmost respect for sports car drivers and I think they are very talented, but I bet a huge number of them would swap out a Le Mans victory for the rarified air that is a F1 WDC.