As a pure developer you always want at least one person just for sales/marketing if that's not your thing and you want your product visible. Even with SEO the "best product" might stay unnoticed. There are exceptions, of course. But betting on making "the next big thing" like that is just a dream of millions that only really happened to a dozen of people. And even in those few cases it's debatable if it was just because of how good the product was.
