Stylization in fashion illustration is still based on an understanding of basic anatomy. Even a drawing with just a quick brush stroke or two requires that those strokes are in the right place anatomically.
I usually start with a structured “under-drawing” either on tracing paper for manual drawings or a temporary layer in Photoshop.
With a structured under-drawing I don’t worry about proportion problems or whether the drawing “reads” correctly if it is extremely abstracted
It is important to draw the structural drawing of the head without hair so the proportions of the face can be drawn in correctly. Then any hairstyle, headpiece or hat can be added in the correct proportion to the face.