Point one: This is not a hunter gatherer society. A highly successful hunter gatherer will do very poorly in today's office-bound society. If you want someone who can only be a hunter gatherer to be successful in today's society, you can't just tell them to "calm down" or "concentrate harder", you have to make accommodations.
Point two: All the creativity in the world won't help when you get bored of a painting, a story, a novel halfway through and can't finish it. Note - I didn't say "don't want to finish it", I said "can't finish it". Just like someone with clinical depression can't just snap out of it and be happy, someone with moderate to severe ADHD can't force themselves to concentrate.
Point three: ADHD does not just affect concentration. Another big impact that ADHD has is on the ability to connect an action and its consequences if those two are separated by more than a few minutes. Funny image -> immediate dopamine response -> fantastic feedback loop. Doing your homework -> discomfort and frustration -> very negative feedback loop.
Now imagine trying to live in a world where doing work and getting paid have no correlation in your brain. You have to intellectualize that doing work leads to getting paid, except you can't concentrate on it long enough to care.