Bah, my tone is still more aggressive than I intend it to be. I didn't mean to turn this into a heated argument, sorry. xD
I'm not saying that in order to ever produce a good drawing, an artist needs to go through years of rigorous study! I'm not saying that any person who does art without having done that studying will ever and on be incapable of producing anything we can judge as "good" until they pass that magical point where they've done enough studies to be considered "good." There is no magical point and there is no precise scale. If I was prescribing that, I'd be trying to support a horribly illogical binary notion of skill that was just completely at odds with reality.
But I don't think many artists could produce art that is
consistently good or appealing without that sort of studying, no matter what sort of art they're trying to do. They won't have the knowledge to be able to deliberately choose what parts of their picture they stylize and in what way. So one time they might hit on the perfect combination of symbols to produce a really aesthetically appealing drawing. Take a look through any teenager's deviantArt page and I'm sure you'll find a gem or two, depending on your own tastes. But the odds of them producing that same phenomenon over and over again get lower the further you go on - you can't just follow a formula you don't understand (eyes are this collection of lines, mouths are this collection of lines, etc. etc. ...) and expect success every single time.
I think most of the great artists that En posted certainly bent, broke and outright ignored the rules in their pictures, and those pictures came out fine. And that's not something I'm trying to argue shouldn't happen! Again, quality is not a binary and the enjoyment of art is subjective. But in order to do the things they did, each one of those artists studied. [nsfw][nsfw]
Salvador Dali[/nsfw] [nsfw]
studied.[/nsfw] [nsfw]
Pablo Picasso[/nsfw] [nsfw]
studied.[/nsfw] Edvard Munch... well, I couldn't really find any works explicitly labelled as studies, but he did
realism too.
The above NSFW links to academical studies and realistic works by a couple grand masters, I marked them NSFW because, well, studies imply nudity.
I'm not going to boast about how I could probably find studies and realistic portrayals from any artist you can name because I know that's arrogant and that that way lies madness, but these are all great men famed for their flouting of the artistic convention of their times. Before and during that, they studied and worked in realistic fashion. I'm (again) not saying that the only good art is art done in a traditional style, or with perfectly correct anatomy, or that art can only be good if the artist has passed some arbitrary point in their studies that now marks them as "good." None of that is true, and it'd be daft to suggest it.
But in order to produce consistently good, appealing art, you either need to be lucky enough to win against the odds despite not really understanding the choices you make in a piece or the symbol sets you're using, or you need to study. And I'm passionate about this because I
never had anyone tell me that. I just kept doodling away as a teenager without any real understanding of what I was doing, and the public idea of "art" as being some sort of strange hedge magic meant that there was never any indication that hey, all the great artists did studies. All the great artists worked their asses off to get to the level of skill they did. And it seems daft to me that I didn't realize that before, but I never had the information. My art has improved by leaps and bounds since I started doing studies, and I'm still just mediocre.
So I guess what I'm saying after all this is that there's no magical formula to get good at an artist, but like anything else you have to put the time in and actually study your medium. ZUN clearly either doesn't have the time or doesn't care to do that - and I can't really blame him, the dude juggles like five different mediums and is excellent in most of them. So he remains a poor illustrative artist. This doesn't mean I'm saying it's bad to like his drawings or that no one should enjoy them! I'm just saying that, at least to me, most of the mistakes he makes are actual mistakes, not deliberately breaking from convention for a desired effect, and that means that whether I'm fond of them or not, to me they're poor drawings.
EDIT: I'm getting the feeling I don't actually understand the use of the NSFW tag.