You’re free to define success for yourself as subjectively as you wish, but startups are held to more objective standards. Nothing in that Mayer quote provided any measure of failure for individuals, so your personal happiness and circumstances shed no light at all on the truth of what she said.
The truth is that hard work and dedication are important components of success, and someone with your same level of contributions who works twice as many hours as you do *at comparable level of performance* will contribute twice as much as you do. That simple math is hard to refute. Easier to refute is the overly simplistic belief that hours worked are a commodity, as though hour 80 is as effective as hour 40.
But you shouldn’t choose a lighter workload and be surprised when someone who worked harder wins the prizes, or, in a downturn, remains employed.