Your points are valid, but ultimately an API is defined by its semantics in addition to data types. For anything beyond extremely primative RPC, you have to rea

Your points are valid, but ultimately an API is defined by its semantics in addition to data types. For anything beyond extremely primative RPC, you have to read the docs anyways. Moving to proto3 means putting all your validation in one place, your serialization primitives in one place, and your docs in one place, instead of smattering them all over. It's a lot less error prone and way more maintenance friendly.