I know it's a myth that we only use 10% of our brain, but the point is that we use less than 10% in any given moment; only by using different parts of our brain for various tasks over time do we ultimately use 100%.
Let's imagine that we have a GPU, a CPU, a quantum computer, and a biological computer that can work perfectly. It's obvious that some of them are going to be better at performing some things than others, but the point is that anything that can be computed can be done by any of them.
I think that similar logic should apply within our brain: Although some areas of the brain might not be too good at processing some things, they could also work towards the result.
What is the reason that this doesn't happen? I believe that it would be a significant improvement in the brain's performance, although it would be very energy consuming.