You can provide no proof, nobody should take you serious.
I don't know, but there are nearly 100 testimonials by professional race car drivers.
https://www.iracing.com/testimonials/
Here are a few.
iRacing is by far the best racing simulation out there. It’s shocking how finely detailed the tracks are; the visual cues and references points are right on the money. And anything you can adjust on a real car you can adjust on the iRacing version and the effects are the same.
Ryan Hunter-Reay
2014 Indianapolis 500 Champion
2012 IndyCar Champion
iRacing is as real world as you can get. The graphics and the handling are by far the best I have seen out of any simulation program. And when I'm not home, I can bet my son, Sebastian, is on it racing someone from somewhere around the world.
Juan Pablo Montoya
IndyCar Series & 2013 Rolex 24 Champion
NASCAR Sprint Cup, Formula One
iRacing is the most modern racing simulation ever created. Every inch of every track is modeled perfectly. I've used iRacing to learn new courses such as Virginia International Raceway, or to keep the rust off at tracks such as Infineon Raceway. For the hardcore sim racer, this is your dream simulation. For the real-world racer, this is your 'at-home' test vehicle.
www.dalejr.com
Dale Earnhardt, Jr.
Monster Energy NASCAR Cup Series Driver
2-Time NASCAR Nationwide Series Champion (1998, 1999)
Any time you log onto iRacing.com, there is a good chance you will be racing against some of the best professional race car drivers in the real world. Trust me, there is no sim site more realistic, with the quality of online racing and, more importantly, the ease of use than iRacing.
Ron Capps
2016 NHRA Funny Car Champion
I have learned some of the Indy tracks through iRacing and it is great to see that the game just keeps improving. The physics are great! Me and my son Eduardo are having so much fun going through the license phases together.
Rubens Barrichello
Formula One & IndyCar Driver
I am very impressed with the realism of the iRacing simulation. Like many of the other IndyCar drivers, I use iRacing to get to know tracks before I even get out on the actual track. Plus it's a lot of fun!
Takuma Sato
2017 Indy 500 Champion
IndyCar / Formula 1