I've only worked at one startup, which was quite successful, and nobody there fit the description of Greg (unless you permute it to be so vague that everybody is Greg). Therefore, you don't need a Greg character for your startup to be successful.
Clearly he is a very impressive person with very impressive results and I'm sure I'd enjoy working at a company with him, or people like him.
I don't like this myth though. Startups are chaos, and pretending that as long as you have this magical person there solving all your problems that your chaos is somehow incorrect. The startup I worked for was full of normal imperfect humans who got offended, had trouble figuring out the direction of the company, were not world-class recruiters, were not always thoughtful and ran into problems big and small all the time. The company didn't die because there was a group of dedicated, imperfect people, who didn't want the company to die, not because there was one "Chief Optimist" holding it all together. If there was a "Chief Optimist" role, it was a very mobile position based on who was feeling best at that particular moment.
This isn't to say you can't and shouldn't actively try to make yourself better [1], you should. But you don't need a perfectly formed person working at your startup for it to succeed. And I want to note, I'm not disputing the existence of superhuman individuals, they exist and I'm sure power a lot of amazing achievements. You just don't need them to succeed, a bunch of normal people can do it too.
1: For whatever definition of better you want, in this context it would probably mean being a better startup founder