that’s only for people senior and above. (small amount of people). 99 pct of people reading this would never get to that level. although you are correct that it used to be the case for a lot more people.
Wow, that's fairly presumptuous of you. Most software engineers make senior (L5) after they've worked in the industry for a few years.
Source: worked at Google and Facebook before.
It's also unclear what you mean by plugging away. If you make improvements to an existing system, you absolutely can get promoted. But on some scale, those improvements are probably viewable as a "new launch", so that's sort of tautological.
Now I am 6 months into another team. I have a good manager on a good team who is unlikely to leave, and I'm on track to get promoted again.