The less successful guy would also "rather" be himself than the other guy, because he too believes the other guy must be trading his mental health for his productivity.
The successful guy doesn't see it that way. He's happy when he sells a car, and he's happier when he sells more cars. He spends his whole day doing his job, maybe even does research at home. He still enjoys his time with his family, has whatever hobbies he invests his free time in (presumably also more successfully than the other guy). He gets to retire earlier, and he knows it, and that gives him more motivation to be successful.
It is absolutely tragic that people can have the idea that less success is more happy. Some people feel better working harder and you shouldn't have to attribute some opaque negative consequence to them to feel better about the gap.
Insecurity itself isn't necessarily a predictor of failure, it depends on what you turn it into.