But the point of the rule is that unlimited growth is not expected. There is a fairly clear point you need to get to, and then you can stay put if you like.
That said, there is an expectation of unlimited growth and it comes from a different source: ageism. At my age, the implicit expectation is that I will apply for a staff or even principal role. Applying for a "merely" senior role often rings alarm bells.
That trend -- and certain others -- are what's making me consider taking up teaching instead.