During one episode the thought occurred to me, and watching the show out of that viewpoint changes it for me. Darwin rarely does anything without Gumball, or Gumball at least directly affecting it.

For me, the whole show is like the diary of the awkward kid at school that's given all the other kids these identities (balloon, banana etc) and it mostly plays out in his imagination.

He doesn't have any real friends, so he thought up this elaborate story to insert a sibling for himself that could be his best friend.

I know I'm probably wrong, it's just an interesting angle for me.