I think you overestimate the amount of senior engineers... even at the extreme end of top-tier big tech, only around 30% can be considered senior. Staff engineers who regularly think at the level GP talks about are 5-10%.

Everywhere else the percentages are quite a bit lower still (if judged by the same standards).

Ya I was very hand wavy. Though in my experience a lot of smaller shops have a higher percent of seniors than big tech. And I don’t know how much smaller shops there are, so I rounded up. Also smaller shops depend more on this well rounded thinking.