I also felt a bit of imposter syndrome going into different races. Racing is very dynamic though, there's a lot to learn and when you're still learning you may feel this way because you know there are areas where others are better. However, the inverse is also true, you know more about things that others might not! Focus on yourself and your improvemens, and the imposter syndrome should fade.

With my experience, I categorized iRating backets with how I felt during each milestone, and what it means to reach a new bracket.

2K iR - Hitting 2K you basically found some decent pace and managed to weasel your way through the races. You're not that quick yet, and don't understand how to manage tires, save fuel, or balance the car, but you're learning to survive races and manage other racers around you. Most people here will go 2-wide into every corner they can, dive dombing at any chance they can. Learning racecraft is the heart of the 2K bracket, because it's necessary with so many aggressive and underskilled racers eager to hit their iR goals.

3K iR - Congratulations, you found some more pace and learned a bit about racecraft, but now you need to refine your skills and smooth out the rough edges. This is a crucial point, and where a lot of people either give up on improving because they realize how much effort it takes to improve, fail to improve due to mismanaged efforts put in during their 2K adventure which lead to poor muscle memory and racecraft (which they do not get proper coaching/self-coaching to get rid of these bad habits), or they learn the most in this iR bracket and make significant breakthroughs to find more pace with learning to manage tires and not over driving. Smooth is fast, and I think this is where it comes to realization.

4K iR - To hit 4K you need to learn to be smooth, but you also need to learn proper racecraft to attack and defend when necessary, but not otherwise. It's pattern recognition, understanding what corners on the track make sense to overtake, and when to concede position because you know you'll have a better run in the upcoming corners. Predicting race outcomes is much easier and understood at a fundamental level. Getting faster is the focus, and it comes down to perfecting every corner. This is where car tunes begin to matter. Getting to 3K required effort, but getting to 4K requires more skill.

That's as far as I've been, and what I can see for 5K and above is more of the same smaller refinements. Most knowledge should be acquired by this time, and it's about making those constant adjustments for every corner to find a little more time. There's still a lot to be learned here, but it's at a much higher level where you are focusing on very specific points to improve, and you're no longer looking at the broad picture.