Well, practice makes perfect. I've been drawing on paper ever since the second grade and my friends say my work looks professional. I did a drawing of Kazooie so good it's on my binder. You see coloring on the computer is much easier especially when it comes to shading and if you mess up, you can go back. On paper, you need a VERY wide color range of markers both thick and thin, a black pencil for shading (does excellent shading) many pens of different sizes, a razor-sharp or mechanical pencil and blank paper. All you need on Paint is a working computer with color capability and knowledge of all the tools.
You see, doing lineart is easy on both computer and paper but coloring is difficult only on paper.
Oh yeah, I have a crush on your art kind of. It's really high quality and you truelly are improving. Hey, maybe one day you can make a manga like I'm doing. You'd do so good, I can tell.