There's no reason to think that a writer couldn't draw a comic. It might look good, but they could still do it.

You need both story and art or there's no comic book. You need someone gifted in each of those crafts. That can be or not the same person but each are as important.

When an artist plot a story he does the job of a writer and becomes a writer. When he writes the dialogue too he is a writer.

Given that some people aren't giften (and lot of them not even trained) to create a story you ever have to get a writer who is a different person or you can't have a decent comic.

Each are as important.

The essential in a comic book is to tell a story, if there's no good or at least decent story there's no professional comic book worth of that name.

A script without pictures is an incomplete comic book, given it is writen to be illustrated,

You can argue that a comic book without a decent story is complete even if mediocre or worse than mediocre, but that simply means that something essential is missing.

-Comic book art is story but to be a decent story it needs a decent writer or if you preffer dreamer and story architect. Comic book is sequential art. And even in a painting, which isn't sequential if it tells a story in one pic you needs a dreamer/architect.

-Reread my posts. It is a question of story structure and of plot, not of script. Script is only a mean to put in shape and/or to communicate a story. If the writer us the same person as the artist and has a disciplinate mind, it can be unnecessary to write a script.

Because you don't take in consideration that a good or at least decent story is essential.

If the artist can do a decent story he is also a writer.

If he can't, he needs one.