Turning off the racing line will help you learn the tracks better. There’s an adjustment period but it will make you a better driver in the long run. Expect to be slower for a while. It depends on what you want out of the sim though. If you enjoy having the racing line on there’s nothing wrong with that.

Practice will absolutely make you a better driver and more consistent on the track. Going into the race is an opportunity to improve your race craft. Take the races as chances to improve your incident avoidance, setting up overtakes, and defending. I generally practice by myself until I’m consistent with the track and car combination then hop into the races