I don’t know if you were here long enough to experience the range of promotion processes, but only the lowest levels of tech promotions are based on individual contributions and ability. To reach “senior” grade, the lowest career grade at Google, requires significant demonstration of leadership. To get above “senior” based on individual contribution alone is virtually impossible. But to rise higher based on leadership alone is quite doable.

I would say technical ability is the least important of the three dimensions of Google’s promotion process for SWEs.