SciFrog:

Why are $75k cars compared to a $200k car? Sorry but no one will be cross shopping these... And for close to triple the price, the R8 better be on a whole other planet of performances.

 Really just no one other that Audi Sport and Stephan Reil.  From the following interview this Spring in Road & Track magazine: http://www.roadandtrack.com/new-cars/first-drives/a33286/2018-audi-tt-rs-first-drive/ 

I ask Reil what he sees as the TT RS's raison d'être. "It is light, powerful, and understated. Super sports cars have a 'look at me!' image. Here you have a toy that performs in the same league, but it's underestimated because it's a compact. It's unbelievably fast on a racetrack. On the Nordschleife, in the hands of a pro driver, the R8 V10 Plus is 15 seconds faster. But with just a good driver, he'll be faster in the TT because of the accessibility of performance."

Additionally, the driver instructors hired by Audi Sport at Autobahn were similarly surprised by the potency of the TT RS compared with the R8 and these drivers have spent vastly more time driving both cars than many posters here.