Earlier quoted context omitted.
Managers are only very tangentially involved with "rewarding" employees at Google. They do not promote them: it's the responsibility of the employee to apply for a promo, though manager has to support. And promotion decision is not made by the manager either: it's made by a committee that has never even seen the employee and knows nothing about their work other than what they choose to put in their "promotion packet"…
In other places without committees most of the same rules still apply. Instead of the committee, the employee needs to justify the promo to the manager+skip(s) and external assessors from other teams often need to also approve promos. I find a lot of the most impactful work isn't easily measured by metrics or monetary impact. These metrics are always deceptive and if you are doing honest maintenance you may encounter…
Even though this system is objectively fairer, it _feels_ shitty nevertheless, I suppose because it's much harder to game through the mechanisms outlined above. You have to game it in other, much more labor-intensive ways, such as "work with" people who are a level or two above you (of which there are very few in remote offices, so you better be in Mountain View for that), sit in important meetings, "show leadership", virtue signal, etc. In fact if you do all of these things really well, you could skip the actual productive work by switching to the management track. If you're not super good at this, you have to do them in addition to your day job, and your promo prospects become tenuous at best beyond level 5.
Regarding metrics, there's a universal law at Google: you can't improve what you don't measure. This is part of the reason why Google sucks at UX for example, and rocks pretty hard at ads and search. The former is not measurable. The latter is.