What? If you accept the premise that talent is actually the capacity/inclination to work harder and practice more, then no, you won't find anyone at the top of their field who overcame a lack of talent. That's the point.
If you're defining talent as some type of natural ability to be good at a learned skill, like playing an instrument, then I think there are many examples of people who weren't especially good at first but became great.
For example, Michael Jordan was good but not outstanding at basketball in high school. He wasn't actually "cut" from his high school team, as the urban legend is told, but as a sophomore, he was put on the JV team when at least one other sophomore was put on varsity. He worked harder and practiced more than others to get better. There are many anecdotes of other players, team trainers, etc., describing him as the "hardest working" and "most competitive" player they've ever met. Did he have some natural ability at basketball? Probably. But people who are close to him attribute his talent to his drive to be better than absolutely everyone else.
Another example is Jimi Hendrix. As a young boy, he carried around a broom and would pretend to play it as a guitar. When he finally got a guitar, he did not immediately belt out Purple Haze. He initially struggled with it as all new players do. Supposedly, he'd practice for several hours every day, often repeating a single note until he could make it sound exactly like a song on the radio. He slept with his guitar. He took it with him everywhere, practicing scales in any spare moments. He'd often go see blues musicians and pepper them with questions about technique. So, did he have some natural ability for the guitar? Probably. But stories from his early life point to his talent being a love of the guitar and a strong desire to master it, in part to escape poverty.
I think the point of all of this is that learned skills take time to master. There are obviously people for whom learning it is easier or harder, and there are physical and intellectual traits that can limit or promote mastery. But for most people, the key differentiator is practice and hard work.
Not everyone can become a concert pianist, but every concert pianist has worked extremely hard to achieve mastery. And most people who practice for hours every day can become very, very good – good enough to play in a band, learn (almost) any song they want, enjoy the experience of entertaining friends and family, good enough for the average person to watch them play and think, "She's so talented at the piano."
