I am actually a professional game programmer. And a *good* designer is definitely better at game design that a coder!

In the same way I read a fair bit, so I am pretty sure I could write a book. I know most of the "rules" of English, I know what type of story I like.

However I couldn't write a *good* book. Just having consumed lots of games/books/films doesn't mean you could design a better one.

Coding & Art & Design are different diciplines, and while most people can have a go at the others most will be only good at one. Some people are good at a couple, and some very lucky people can do them all.