Doodle Diaries: I don't know what is wrong with my drawings plz help, part 2

(Continued from Part 1)

TL;DR summary: I am really, really bad at lining and coloring my drawings on the computer, despite doing everything that I should be doing. My drawings look okay enough as pencil sketches, but look flat and amateurish once I line and color them.

(Exhibit A: my drawing from July, and a quick replication done by pencil on Dec 31)

After the whole series of critiques from last time, I watched a bunch of lining and coloring tutorials and speedpaint videos on YouTube, just like I did when I first began drawing digitally.

I haven't missed anything; I already do all the things that the videos do. But everyone else's art looks great while mine does not. I do not understand this fuckery.

I was starting to reach the conclusion that my drawings "just suck". Hear me out, I have actual reasons for saying this:

1) My lines just don't look nice and I have trouble with making some parts thick and some parts thin, which adds dimension to drawings.

2) I suck at picking nice colors. Color combos have not been my strong point since childhood.

3) I still suck at details such as clothes folds and clothes wrinkles and skin folds and hair parts.

If this is really the reason that my drawings don't look nice, there isn't much I can do other than draw more until things come out right.

So I tried another test drawing. My goal this time was to do the usual things I do, but 1) be super meticulous with colors, and 2) be better about details like hair and clothes.

Process summary below.

Lineart

Flat colors

Shadows and highlights

Colored the lines instead of having them black

Huh.

Wait.

The end result... doesn't look terrible?

I created layers upon layers for this drawing, constantly adjusting color levels until it looked "right". Was color choice my problem all along?!

I need to try another drawing.

I used an old, old doodle I did on scrap paper in 2016 as reference. 

Lined, colored, background, colored lines.

The drawing looks less refined since I used an old doodle for reference, but this also looks okay...?

So color choice and details are indeed a few of my problems.

Next I tried to work a bit on lines: I used a vector layer to line my next drawing instead of a regular layer, and tried to adjust line thickness.

Yes, I am absolutely going to use every pattern on CSP as backgrounds.
I also forgot to highlight their hair but I spent too much time on this so I'm moving on.

The left looks fine with the black lines; I needed to color the lines on the right for it to look the way I wanted it to.

So lines may also be a factor I need to pay attention to as well.

...

I guess the primary problem with my drawings was that they indeed "sucked" and I need to be more meticulous when I draw.

Okay then.

Whoever said "Drawing digitally makes your drawings look less crappy because you can color them in which hides flaws" needs to have a word with me.