I would say that talent is how good you can be at something without having to try (i.e. without hard work), and that as such it is a continuous quantity rather than a binary one. When talent runs out, the only way to get better is through hard work. In a way, I think being too talented at something is a handicap because you never learn how to work hard, and so you are unable to progress any further than your talent will take you.
if luck is "success against the odds", the odds are dramatically improved by making several attempts, and making adjustments after each one. In these circumstances, I'm inclined to say that luck is inevitable.
That Dweck book is indeed a good one, if not a bit touchy-feely in its take. It's really important finding in Dweck's studies that this mindset distinction has a huge effect in the effort people make. The people who believe they're bound by their inborn talent (fixed mindset) do not push hard and usually just give up when hard problems come up. People who believe the opposite (growth mindset), that your abilities are not constrained by your inborn talent, tend not to give up when things get difficult but just put more effort until they actually do manage to solve their problem.
So, in this sense it's actually irrelevant whether or not inborn talent is necessary, because the mere belief that it is could have negative effect on your effort.
