Your code speaks for itself only to people who care about code. Which, as it happens, doesn't include a lot of investors, co-founders, customers, employees, and all of the other people you're going to have to persuade if your startup is going to be successful.

Heck, even if you have a "smarmy sales-dude" as a co-founder, you'll still eventually be in a role where persuasion/leadership is more valuable than coding chops. What percentage of successful startup CTOs do you think code on a day-to-day basis?