Also kind of insane. 1-2 years? In any large codebase or platform, it takes a year to become familiar with and touch a decent portion of it. Also, talk about never having to live with the concequences of decisions you've made in terms of long term support and maintenance. But I guess these are all rockstar developers doing the hopping around so that's not really their concern is it.

It's usually closer to 2 years than to 1.

I would say it's better to do 2-3 years early on as a young employee. Older, more experienced tech people tend to have longer tenures as they gain years of experience.