Both arguments can be (and are) right at once.

What OP said is definitely true on the micro level-- not "even/might/some aspects", but the whole thing. It's true that in any given organization there are fewer senior roles because of hierarchical nature, it's true that as you progress up the ladder the demands change and increase, and it's true that many people fail or choose not to adapt.

The macro argument seems right as well. If you measure it longitudinally the numbers don't stay constant. It's 1 in 4 today, maybe it was 1 in 10 fifteen years ago. Anecdotally there is definitely something strange going on with the labor market that's new, and that you can't explain by micro realities alone.