Why do you feel the need to simplify life into such a narrow perspective? While it's true that being smart can limit your confidence, what you've written is beyond exaggeration. There is so much more complexity involved.
This is largely my experience as well. The Bay Area wannabe startup crowd is brimming with idiots, people dumber than your dumbest colleague at work. Unbelievable amounts of Dunning-Kruger.
The actual grind filters out most of them, of course, but if you concede that some businesses are basically luck then some number of those idiots will make it.
People who don't have those types of things in mind can only be so smart in my book.
Having access to capital is much more important than smarts, which is why so many people starting businesses have generational money propping them up, or as a safety net. Even smart people are usually reliant on that family capital. Bill Gates’ parents were millionaires, Musk and his dad’s emerald mine, Thiel started his first hedge fund with a million dollars raised from “friends and family”.