> using an interchange format like protobufs allows for automatic client generation in several languages

Maybe things have improved, and maybe I was using the "wrong" languages, but when we tried this at a previous company the generated code was deemed so awful that we abandoned that idea almost on day 1. To this day I tend to believe the promise of "write once, generate anywhere!" to be mostly BS.

Not even picking on protobuf specifically here - last time I tried a REST generative approach (swagger?) the results were similarly unusable. The whole concept is a fantasy, unless things have staggeringly improved.