It's important to understand that, despite having the same names as traditional media, the tools in ArtRage and any other program are not going to be the exact same. What works for one thing, may not work for the other. If you must base your judgement on time, then think back to how long it took you to learn a specific traditional media to your satisfactory, and allow yourself that same amount of time to learn to do it digitally, and be honest with yourself about that time. It may have taken a few months to learn how to use oil paints efficiently, but if those were months spent in art course, where all you did for 8 hours of a day was paint, you should account for that.
The precision will come with practice. The understanding of art fundamentals... That may be solved with some good books, classes, and even online tutorials.
Nothing is easy to the unwilling.