https://mtlynch.io/why-i-quit-google/
As always, this is my single-sample personal view, so please don't mistake this for anything beyond that.
It's true, we do place a lot of importance on complexity and impact, which are fuzzy metrics, potentially inconsistently defined, and can be subject to circumstance. Yes, engineers do suffer the temptation to game things by releasing their work prematurely and not committing themselves to supporting it. And yes, not all managers know how to set expectations appropriately, occasionally resulting in disappointment and confusion for their employees.
However, that's the individual's perspective. Promotions serve the institution first, and the individual second, and I'd like to offer the institutional perspective.
Promotion to senior engineer is a big freaking deal. Once you are Senior, you've effectively been given the keys to the kingdom. It's the industry equivalent of tenure. Want to transfer to a team? No problem, your manager knows they're going to get someone who's been through hell and is able to deliver. Want to join another company? Great, "Senior Engineer, Google" is an indisputable mark of quality, you'll at least get an interview.
If there's one thing I've learned in my time here, it's that false positives are way more costly than false negatives. Hire someone who can't do the work? Enjoy six months of trying to grow them plus however long it takes to get them to leave and release their headcount. Promote someone who isn't indisputably good enough for the title? Enjoy watching them fail to meet expectations cycle after cycle, trying to grow them, only to watch them leave out of frustration a year later.
Yeah, it kinda sucks as an individual contributor because proving yourself is difficult and subject to external forces. That's torture for the sort of ambitious overachievers that tend to be drawn to this company. However, the thing that makes your career growth difficult is the same thing that makes the work so challenging and the work environment so pleasant.
Also, there are some recent developments the author didn't mention, and I presume he left after this was put into place. A lot of focus has been drawn away from the rank of Senior. On paper, things used to be "up or out" until Senior, even though that wasn't really applied in my experience. Now it's only "up or out" until L4, one promotion below Senior. Plus the Senior promotion process is getting streamlined somewhat, although time will tell how that plays out.
EDIT: And then there's money. Managers have enough leeway that overachieving L4s can make almost as much as an L5, so it's not like the lack of a promotion is impoverishing you.
EDIT EDIT: To give some more context on the process itself:
For non-promo candidates, we do mutual reviews. You list the colleagues you'd like to review you and list the projects you've worked on and your contribution to them. Then everyone comments on their colleagues' assessments.
Managers then get together and have a powwow in which they agree on who in their groups are giving exemplary performance at each level, and people are calibrated as above or below the models for their level.
For promo candidates, the self-assessment is much more in-depth, and a committee of unrelated people get together and perform a similar assessment, except against a more abstract rubric describing expectations at each level.