>>5479202I'll try break it down a bit.
When someone asks you to draw them and you draw the generic almond shaped eyes, a nose, draw their head as a circle etc you are symbol drawing. You are not drawing what you see, the lines, the folds, the contour of the skin and the shadows on it. You see an eye and draw an eye, or rather the 'symbol' for an eye. It is not that person's eye, if overlayed it wouldn't line up with it but it is recognizable as an eye. It is a symbol for one.
Advanced symbol drawing is what I call it when people skip over the fundamentals and by grinding eventually get better at symbol drawing. You don't have the fundamentals and don't have any transferable skills because you spent time grinding symbols instead.
To compare it another way I don't know if you did it but in school I'd draw a 'realistic' eye. I'd draw the same eye again and again. Sort of as a sly way to try impress people dumb I know. I got what I thought was decent at drawing eyes. But I wasn't. I didn't improve my findamental drawing skills and was wasting my time being better at advanced symbol drawing of one eye in one very specific pose.
Drawing anime is a trap. If you sit down to do a study you'll see how little you've learned. I have no doubt you are working hard. Put that effort in the right place and study like manga artists do.