The way to get promoted at Google seems to be to play a game where you tick all the boxes for performance at the next level and have the right people write for you. In some ways, that helps the company (working across teams, for example). In other ways, it may hurt the company (launching potentially redundant products is seen by committees as being more valuable than incrementally improving existing products). I think that a lot depends on who writes recommendations for you in your promo packet (and that's pure politics)
In my case, I was basically gathering requirements and helping other teams integrate with an internal product. So I was perfectly positioned for promo. I was an L5, and talking to a lot of senior folks in other teams (sr. staff, director, vp) who were willing to write for me. I'm pretty sure having a VP who knew me and could write about me really made the difference.