There isn't anything functionally special about the human brain - why is there some reason to expect the human brain is capable of innovation but no program, even one far more powerful than the brain, is not?

You admit this possibility so I'm not arguing with you, but it seems far more plausible to me that we can build something better than the brain.

In the limit we can just grow brains and put them in computers anyway, then the debate is moot. That's a really hard problem but of course not physically impossible.