You seem to forget that the guys in the second Audi brought it home in second at Le Mans, and disregarding their other accomplishments (Super GT and FIA GT)
And aero is a big part of it--the Pugs at Spa ran in high downforce trim, and that keeps more heat in the tires on a cold track. You also seem to be disregarding that Sarazin is an ex-rally driver. Pagenauld in the winning 908, even with the high downforce package, nearly buried it in the gravel on a damp track.
Audi's drivers themselves even say that the R15 is much easier to drive with the high downforce package. But is it faster? Aero is just part of the issue. At PLM, the Pugs were on edge if you ask me on handling, but that's maybe what makes them fast. I also think that Peugeot have moved away from the rock-hard F1 suspension set ups (aside from Le Mans), as the J-damper does the job just fine on its own. Sportscars have one thing that F1 cars don't currently have--low profile tires.
On F1 cars, and even NASCAR stock cars, the tires do a fair amount of acting as a suspension medium. On sportscars, the low profile tires don't allow much for that. As a result, the Pugs did tend to be edgy and hard to drive on bumpy tracks like in America. This year, it seems that Peugeot has finally learned that lesson, which they ironically gleaned from Audi on how to get the ballance between stiffness and compliance.
I think that's helped Peugeot in the rain, but at Silverstone in the wet, the Pugs still seemed to be a handfull in the wet. Nevertheless, Peugeot has learned that building suspension that's filled with concrete can't be relied upon to get the job done.
By the same token, it can be argued that Audi needs to re-learn (from the R8) that "loose is fast", because the Pugs seemed to be loose in fast corners, but it was controlable. Audi says that the R8 had very slight understeer which could be managed by power oversteer.
Audi should look to the past for their success, as the more conventional 908 is still competive with the theorietically more advanced R15. The 908 has emulated the R8, and maybe Audi should do the same instead of going on a whim and trying to build an oversized LMP2 car like what Acura tried to do, and we know how that ended for Acura.
In short, Audi needs to focus on getting the car mechanically hooked up and using the areo to enhance it, instead on using LMP2 areo fads.