I’m personally tired of this ass backwards argument.
Of course it’s possible to understand how brains work. It’s called science. We (collectively) are well on our to understanding the biochemistry of neurons and brain structures.
Everything exists in the same universe and follows the same physical laws.
That we're so early in this cycle doesn't mean it's impossible.
The good news is that there is a lot of evidence that computation in the brain is more modular than that... It's not necessary to understand each neuron... Just like it's not necessary to understand each artificial neuron in a large nueral network.
However, I entirely agree with the sentiment: We don't necessarily understand brains now, but we don't dismiss their capabilities just because we can't explain precisely how they do what they do. By the same token, complex tools like deep learning shouldn't be dismissed just because we can't satisfactorily interpret them.