Basically, that whole eng ladder thing is really important. I looked at that a lot for my own promotions and for evaluating candidates for promotions. Just dealing with churn isn't really on there, so it's probably not something you should focus too much on. I'd say that's true at any job; customers aren't going to purchase your SaaS because you upgraded from Postgres 12 to 13. They give zero fucks about things like that. You do upgrades like that because they're just something you have to do to make actual progress on your project. Maybe unfortunate, but also unavoidable. Finding a balance is the key, as with anything in engineering.
The biggest problem I found with promotions is that people wanted one because they thought they were doing their current job well. That isn't promotion, that's calibration, and doing well in calibration certainly opens up good raise / bonus options. Promotion is something different -- it's interviewing for a brand new job, by proving you're already doing that job. Whether or not that's fair is debatable, but the model does make a lot of sense to me.
Things could have changed; I haven't worked at Google for 4 years. But this was a common complaint back then, and it just wasn't my experience in actually evaluating candidates for promotion.
