I have seen however people who start as mediocre, writing competent but frankly boring books. Back in the day when midlist was a thing, many of them stopped after one of two books. Some, however, persevered, honing their craft, selling just enough to be picked up for another book. A few of those became truly exceptional authors, where their book 30 or forty actually became one of my favorites of all times (and won awards, etc.) Only a few, but it shows there is more than one path to greatness.
Sorry, I should have clarified, but by "born into it", I meant your second category, those whose story shows promise. For everyone who has the capacity needs to keep at it, as it takes a long time, both to learn, and also to hit on a winning combination that captures the public eye.
In the old days of traditional publishing only, we never saw anyone until they'd been writing for years, honing their skills, now we see the raw talent, cranking out weak novels as they struggle with their craft, but generally, you can tell by their very first story if they're decent storytellers or not. Plus, with a big publisher, a decent editor can make a world of difference (assuming they get along well).