Ok, so let's think about this for a second...Darren Hardy is a "Success Mentor". He's a motivational speaker.
Would any motivational speaker say "Some people just don't have it"? Of course not!
At the risk of coming off wrong, I have to be super super blunt here: Some people just don't have it. Just like you would never attempt to become a professional football player, or the world's greatest singer (without natural athleticism or a good starting voice), someone who does not have some base level of innate intelligence should not try to make it to MBB. Their time is better spent elsewhere on other things.
We "trade" in ranges. A lazy smart person lands at the bottom of their range (they have a high floor). A hardworking average person trades at the top of their range (they have a low ceiling).
Hardwork helps to make up for lack of innate talent but does not replace lack of innate talent.
I'm sorry, but I've found that 100% yes or 100% no answers are rarely right in life...it's a scale and it depends.
That being said, there are plenty of people who have worked their way into MBB and openly admit it. Still, they are still at a minimum moderately intelligent people!