Protos is more of a faster & smaller network serialization tradeoff vs. ease of development thing than a company scale thing. And a thing to do if you want to integrate with gRPC.

I worked at a company that used protos from day one for example.

Many large companies are still using JSON w/ schemas as their network serialization layer just fine.

I'm not familiar with the Kotlin build chain, but what role does Bazel play? Is it needed for integration with the protocol buffers?

Yes - Bazel has excellent protobuf integration compared to other build tools (we were originally using Gradle). We're compiling Kotlin to the JVM, so the build chain is similar to Java's.

Gradle has a great protobuf plugin, what is so not excellent compared to Bazel?