At some point, the cargo cult are the promo reviewers and then the two become the same thing.
Senior engineers will:
* Design a significant project which lands with measurable customer impact
* Demonstrate expertise in at least one core skill outside of coding (test infrastructure, SRE, security, accessibility, etc.)
* Demonstrate leadership by either being a TL, owning and leading team pillar efforts (security review, etc.), etc.
* etc.
Mid-level engineers will:
* Own either a small feature end to end or a significant piece of a larger design
* Contribute to at least one non-coding pillar
* etc.
These generally have more areas and can be further granular such as "low-performing midlevel is X, satisfactory is Y, exceeding is Z"
Just proves the point, this person just cargo culted what makes google so famous in recent years. If you only metric is to launch new projects, you’re only gonna launch new projects. Who’s gonna get promoted for maintenance.
Again, not trying to debate what the specific bar should be, just giving examples of the kind of metrics you can use. What's your preferred alternative? Lines of code? Whenever your boss feels like it? Stuff like that is why no one believes a "senior staff superstar" from the hot startup of the week is any good and requires them to do whiteboarding.
Thus, there are rules, and they are written down. If they're not visible to normal employees, they guess the rules based on who they see get promoted (cargo cult) while the committee uses the true metrics.
It's not like becoming a manager is a secret cult where you're dropped in and you suddenly have carte blanche to do anything. At established companies there are rules and procedures, and while you will likely have access to more information than individual contributors, you won't just be promoting whoever you feel like without having to go through others.