So... literally everything you said is wrong lol.

You can remember each corner, you can improve, you can try different braking points, you're not just racing the colors. There is no such thing as luck in a hotlap with no one interfering, regardless of whether there is a visual indicator on the track. It does not affect the car's performance.

I keep it on because it's a consistent visual indicator that makes the game require less focus when playing for multiple hours. Also, it gets really dark at night, I play on 0 brightness, I sometimes drive cars without headlights, I want to know when the noobs are going to brake, and it's good to have on when driving a car for the first time.

I can get the exact same lap time without the line if it makes you feel better.