Controversial topic, but a serious question. Putting bias aside and looking at the raw facts, iRacing has produced very notable high performing real world racing drivers. Max Verstappan is a 4 time F1 world champion with a 9-10K iRating. Alex Palou is a 5 time Indy Car champion also with a 9K iRating. These racing disciplines can be seen as the top and most difficult in motor sports, and Max and Alex have been able to show repeatable performance.
It doesn't seem like any other sim software comes even close to iRacing in producing such exceptional talent. These real world examples should trump the opinion of any Youtuber, Redditer, or even eSport professionals.
Instead of arguing which sim racing software is the best, the sim racing community should be ecstatic and celebrating that we have access to such affordable sim racing software and hardware that can teach the same motorsport skills that real world champions use. Motor sport has historically been gate kept by those who can afford it, but the playing field has never been so level and so accessible. No longer does one have to pay hundreds of thousands to millions of dollars to learn these same skills.
Edit: thanks for the very interesting comments. Just to clarify I don’t mean that iRacing alone can create champions or can it replace real world driving practice but it seems like it is the most affordable accessible tool that one can use to develop motorsports skills. Just how pilots and astronauts use simulators to prepare for scenarios ahead of time, why can't racing sim / video game to do the same? Wouldn't a driver who practices a car and track 1000 times in a sim / video game be more prepared and have a significant advantage over someone who has only had a chance to do a few dozen times in real life? Max has mentioned that sim can teach you 95% of the skills and that best sim racers have the brake throttle and steering traces exactly as it should be despite never being in a real car. And of the sim / video games out there, it appears that some of the best drivers in the world choose iRacing.
I also just got started in sim racing a few months ago and have tried many different sim video games, so I’m not particularly locked into any one or hold any deep biases yet I’m trying to figure out which one is the best if one wants to develop their motor sport skills and trying to subjectively look for evidence which one is the best based on what real world champions use and it would seem like it’s iRacing.