Ahh cuz those are two different styles. YoungCutthoat is a beast with both techniques. Now the Cham/E-40 ones I did are more of a combination of coloring and using the burn/dodge tools as you can see
here and
here. The vector style GTA look is like
this and
this or
this. Now I'm not an expert or anything but best tips I could give you is take your time, be patient and practice because it ain't coming to you over night. Learn the pen tool and brush control. Also pay attention to detail, break down sections and simplify it rather than trying to recreat a masterpeice. You'll get to that point where you can just bang shit out, trust me.