If the Popits work well for you, why put so much pressure on yourself to do it the "traditional" way? Don't be discouraged! I have been a tech for 11 years and still have days where I feel like I am doing a poor job - although the clients don't seem to think so!
It takes a lot of time, practice and patience to perfect your craft - so don't be so hard on yourself. Learn with the Popits if you like and practice the traditional way until you are comfortable!
The traditional way is beautiful - a real art form in my opinion. However, I may never hand scuplture again if I can get away with it, as time is money and the Popits cut my time by over half! Why wouldn't you utilize a product that gives you beautiful results with hardly and work? Sounds like good business to me! The colored powders I use normally require a clear cap of l&p as you cannot file directly on the colored powder or lose the color. With the Popits I don't have to clear cap - saving me product and time as there is almost zero filing. Or, I can choose to have the first layer in my Popit be clear, add the color behind it, and still have no filing! Its a gift from the nail gods!
Chin up - with time and practice you can do this and do it well!