I’ve never worked in SV. Only small enterprises, Microsoft, a handful of local startups, and one SV company. The SV company had above average retention compared to most of the non SV places I’ve worked. The 3 year range has been pretty much the norm in my experience (20 years or so). 5 years has been on the high end in every company I’ve worked for. It is anecdotal, but it is what I’ve seen consistently across markets both large and small.