There's one way to get to the facts regarding this: Arrange a race in which the setup is enforced to be identical for all drivers.
You have good and bad tennisplayers, you have good and bad simdrivers.
With Tennis, it's easy to spot why someone is better than you. He has better ball control, hits harder, runs faster and problaby makes fewer mistakes. All these things are expressed very clearly in points.
Summarizing: everyone understands what the difference between a good and a bad player are.
Now, let's turn to (sim)racing. You practice your ass of for days to learn that some guys online are 3 seconds (i.e lightyears) ahead of you. How is this possible?!! How can this be, when you know you are on the very very limit at every braking zone and in every turn. Surely they must have access to a secret that is not known to you. Cheating would be unlikely, so, problaby it is the setup. No way they would be so fast with your setup.
Guess what: wrong. In Tennis we could see what makes a good player. But can we in sim-racing? What makes you faster? Is it really braking that late, hanging on to your life at every corner?
From my experience, as well as from competing against the world's fastest drivers in iRacing, people (myself included) rarely understand the technique of going fast. Sure, we all take a turn outside-inside-outside. But there are so many more subleties, so many more parameters that make a difference. I believe the secret aliens have is most and foremost understanding the simple fact 'how to go fast'.
Second, they have the ability to actually do with the car what they have in mind.
Third, and least important, they usually spend time perfectioning their setup, commonly with equallyfast drivers in 'teams'.
Concluding I can only offer one advice: analyse your own driving and win tenths, if not seconds.
Two beginners tips often overlooked:
1) watch a replay of your lap. Do you really use every micrometer of the track at entry, apex and exit?
2) when you have established the absolute latest point where you can brake snd make the turn, now force yourself to brake 5 metres earlier and see your laptime improve significantly.