If you need assists then use them, but the goal should be to get off them as soon as you can. You will be faster without the assists but most importantly you will learn how to control the car and learn the tracks better and permenantly without them.
Lines are an especially bad assist to continue to use but I do occasionally use them on a new track to get in the ball park but I am using them differently. I go around the track finding the flow and roughly where the car is and looking at what the line thinks is the brake point and using that to find a reference. After a few laps the line goes off and I don't need it, I want the information in it to give me an idea of the rough areas but then I evolve from there. The main problem with the line is it disappears under the car ahead and are very hard to find the brake point while it's under another car making it dangerous online. It also doesn't give you a good brake point for overtaking and you will invariably get this wrong since the line isn't helping, you need to train the other cues in your brain to get that right and it can't happen while the line is on. The reason people use the racing line is for the brake point. You can use references on the track as the brake point instead of the line, just find something nearby the lines brake point (travel slowly) and then try without the line and you'll be surprised how much you know. There is a good chance on some of those points you already know to brake later or lighter and so you are only using it as a reference point as its missing a lot of the key details you need to go around the corner well.
As to other assists, it depends a bit but they all slow you somewhat. Traction control and ABS above what a car provides can be beneficial for staying on track as they stop a heavy foot from ruining your race but also take away the characteristics of the car and do slow you down a bit. Automatic shifting gears is definitely slower than manually changing. Auto blip/Auto clutch has a small impact too.
Don't just give it all up at once. Remove something and work on it and then the next and the next until you have removed it all. There is no substitute for time when it comes to driving and it takes a lot of hours to train this very unnatural skill. Take it one step at a time. Get rid of the line first, that is the one that will help the most with just generally driving the right way.