>>3603777as a grader I can at least tell you that 90% is the original. people who start grading are sometimes frutrated over their results, especially when using their own material and especially when their originals are not very well done in regard to colour design, lightening and composition.
a well done original grades more or less itself. and then it is absolutely true that you only make tiny adjustments. beginners also tend to overdo grading. which they have to do especially when they have blant originals. a vicious circle.
if you want to do only grading without shooting your own material then look for good shots out there to train. have a good monitor which is able to represent tiny adjustments.
if you want to shoot your own material, try to produce shots which you think they wouldn't need grading at all. then look at the tiny perfections you still can do and grade them. then you will see why there is not much to do. thou you have to do the right things, but not much of them.