>Is it not more likely that most historically successful people just stumbled on the promising gaps almost by accident?

to some degree, but it's not like you can luck your way into writing an app by slapping the keyboard. The degree of success might differ, but generally there's some kind of barrier of entry in terms of the work to learn the base skill needed. Right place at the right time is a thing, but plenty of people miss out because they don't even try at all