I have seen plenty of people that work on existing products like Chrome, Gmail, etc. get promoted. I also have witnessed people successfully going from L4->L5

I have seen plenty of people that work on existing products like Chrome, Gmail, etc. get promoted. I also have witnessed people successfully going from L4->L5 as SWEs without launches. I had to see to believe it, and I have seen it. That said, Google is a GIANT company, and other people might have different experiences. Disclosure: I work at Google.