Theists have a 101 different interpretations of God, so it seems the "misunderstanding" is not of an atheist's making.
Also, atheists don't make the assumption that God is complex, they make the assumption that theists suggests a complex God to explain the complex universe. Perhaps it's a misunderstanding between them two, or perhaps it's the lack of explanation and definitions available to the theists to really describe why something complex must have a "God" to create it but isn't complex in itself. Essentially, it's not the atheists' view that God is complex, but many atheists get that impression from the theists (mostly Christians).
The argument tends to go something like this:
C. The universe is too complex not to have a creator
A. So you're saying that there has to be something or someone more complex that created it?
C. Yeah.
A. Then why doesn't God have a creator?
...
Now we're learning that the proper answer from the Christian should be: No, God is simpler than the universe.
Now, it's just a matter of making all Christians and theists to know this. God is simpler than the universe, that's the word.
The funny thing is, I can't help but think of the Singularity at this point.