Ah yeah, I think the historical issue is that Google doesn't use std::string internally for performance reasons. They have their own C++ string implementation,

Ah yeah, I think the historical issue is that Google doesn't use std::string internally for performance reasons. They have their own C++ string implementation, which protobuf uses internally, like all other code. And then when they open sourced it, I guess they left out that code. So the open source version is probably "de-optimized" a bit unfortunately.