I believe it makes about half of that difference (5-6 secs a lap), and that is a thorough understanding of the game physics, and that means good and bad, everything, temps, track temp, outside, wind, aero, shocks, the works.
Good FFB knowledge and gear, a decent screen setup and PC.
Over a guy with similar pace initially, all that will gain considerable time, the other guy with practice will get there, and get consistent too, but he will never gain the time the guy with the best kit and knowledge can get.
I liken it to safe and aggressive setups, safe is never quicker, no matter what to the same driver who has got to a level., and this is what I mean, you are seeing the evidence in front of your eyes.
Get telemetry from one of the guys who "do nothing better than you but have a better setup" and you'll see that you simply suck in comparison.
I was lucky to occasionally get telemetry and setups from very fast people and it was always just me who sucked, no magic setup.
Sure, with an oversteery suicide setup that bounces at every kerb it won't be possible, nor with an understeering ship like setup.
But from your mentioned 5-6 seconds, maybe 1.5 are down to the setup.
And sure, some people will invest a lot of time into the sim, but maybe they are just more efficient in learning, practicing, visualizing things etc.
My best friend and I both play guitar. When we're practicing a new song to play together he sometimes gets frustrated about me learning the difficult parts so much faster than him.
I then remind him about my 200 hours of finger training with a metronome that I've done over the last 10 years.
He never did any of them.
Now he plays more than me since about 2 years but still never did efficient finger training routines so some things won't improve anytime soon.
So maybe these fast guys do spend a bit more time in the sims. But maybe they had a way better starting point than you.
Or they're just more efficient.
About equipment: seeing more (monitor/vr) makes it easier to learn a track or battle in a tight pack. But once you're at a certain speed level and just hotlapping, you don't need to see more or better. You just need to remember more track markers instead of only taking in what you're seeing in realtime.
Same for wheels and pedals. Better equipment let's you feel things better in real time so you can get faster... Fast.
But once you're down to only improving every tenth lap during practice, this difference diminishes.
There's one thing that I have to say about getting better wheel and pedals:
If you never felt some ffb signals in your life, you won't be able to "detect" them on a weak wheel.
When I upgraded from g27 to fanatec csw 2.5 I wasn't faster around the Nordschleife. Not even half a second.
BUT then there was that one corner before Schwalbenschwanz (second carrussell) where you're dancing on the brakes and throttle at over 200 km/h.
With the fanatec wheel I could feel the increased grip from the working aero.
I gained 2 seconds in that single corner.
But nothing throughout the rest of the lap...
I also "unlocked" to feel the front tyres getting loaded when braking. Feeling the weight shift in the ffb strength.
Got a lot faster in the BMW 235i.
Then I tried the g27 again and what should I say?
I could feel the aero load at the Nordschleife and also the weight shifting.
It was a lot more subtle but now that I knew how both feel like, I could feel both things with the g27 and got just as fast...
With pedals it's different. As long as your body is precisely enough, pedals above the Logitech ones don't make you faster.
But a lot of people simply can't be precisely enough for g27 pedals for example. Not enough resistance.
I didn't really have any issues with them. Driving in socks and being young and used to the super light pedals from today's road cars.
But when my dad tried my setup he just stomped on the pedals. It looked pretty "digital". 100% or 0%
So if you suck or are physically handicapped to be precise enough, then pedals make you faster, yes.
A better wheel can unlock new ffb stuff. Once unlocked you don't need it anymore though.
You can also unlock it by doing a driver training, practicing with a real kart etc.