There are multiple characters with natural-born talent, but for many of them it has been expressed that this has not enabled them to succeed or is not the only thing that has allowed them to succeed.
First, there's Big Mom's fellow Yonko Kaido, who's a lot like her in that his body is so tough that no one has been able to kill him. Said super strength didn't prevent him from being defeated 7 times and imprisoned, put on the execution block over a dozen times.
Then there's the Cover Story star, the pirate prince Cavendish. His alter ego Hakuba gives him unprecedented speed and power which few can withstand, but he hates Hakuba's bloodlust since it's the complete opposite of the image he wants to cast himself in, plus Hakuba is dangerous against everyone rather than just his enemies.
That's not to mention Sanji's brothers, whose plight we are well aware of in this arc. They were true child geniuses, essentially becoming as strong as adult warriors while they were still young. But their incredible development made them oblivious to the consideration of strength through hard work, and gave them a superiority complex to Sanji which is currently being put through the wringer right about now. If anything, this arc has hammered in the point that hard work can get results just as well as natural talent, and the experience often leaves the hard worker better off for it.
There's also Shirahoshi, who's quite a bit similar to Big Mom in that she's ridiculously large and had an emotionally stunted development. While she hasn't suffered effects as bad as Big Mom has, it's clear that she'll have to mature significantly in order to use her power well.
While Big Mom has obviously benefitted from her natural strength in the long term, her upbringing has left her with certain weaknesses. Her people skills are still shit and her crew is pretty dysfunctional as a result. She has an unhealthy attachment to food which causes her to go into a destructive state that's far worse than Hakuba's. She's emotionally immature enough that she's placed so much value into a picture that she becomes completely weak when it's gone. These traits have all prevented her from taking the final steps to success, and have come to bite her hard against the very savvy Firetank-Straw Hat Alliance.