I think he is referring to the fact that you use a fluent builder interface when building protobuf messages so you chain together a bunch of `.setFoo(myFoo).myBar(myBar).build()` to build your protobuf, while in Kotlin it is idiomatic to write `foo = myFoo` and `bar = myBar`. There are ways around this with `.apply` in Kotlin, but it all feels really clunky.

That said if you want a systematic don't make me think approach for backward and forward compat I think protobuf/GRPC is the way to go you just need to learn a few rules for how to do it and you're set. In terms of static typing protbuf doesn't really get you that much because in order to get backward/forward compat you can't have required fields, so everything needs to be null-checked or have default values.