Using Airbnb as a reason why your idea doesn't matter is like using Bill Gates as an argument for dropping out of college. The idea is super important; in Twitch's case, the process of getting to that idea was putzing around with something terrible for a while. Ideas do matter and you're not doing anyone any favors with this quixotic reductionism.
Clearly the idea (or the solution) is important - my argument is that knowing the right solution day one isn't very important. Airbnb and Twitch are great examples of this.
You're extrapolating from the winners and applying that to the masses. Read up on their history; Airbnb and Twitch almost died multiple times and that's not a good model for any startup. Even startups that actually start with a good idea fail frequently.
