protobuf is more friction, and actually slow to write and read.

For better or worse, CSV is easy to produce via printf. Easy to read by breaking lines and splitting by the delimiter. Escaping delimiters part of the content is not hard, though often added as an afterthought.

Protobuf requires to install a library. Understand how it works. Write a schema file. Share the shema to others. The API is cumbersome.

Finally to offer this mutable struct via setter and getter abstraction, with variable length encoded numbers, variable length strings etc. The library ends up quite slow.

In my experience protobuf is slow and memory hungry. The generated code is also quite bloated, which is not helping.

See https://capnproto.org/ for details from the original creator of protobuf.

Is CSV faster than protobuf? I don't know, and I haven't tested. But I wouldn't be surprised if it is.