So in that sense they aren’t all that modern as they’ve failed to evolve and keep up with platform evolutions.
Bebop just aims to generate code that modern and current with its target language, works everywhere, and avoids pitfalls protobuf suffers from.
Even though our schema was huge, it still did serialisation in a time that was surprisingly small for our underpowered chip.
I can't speak for Google's official implementation though.
Also I tend to want generated code to be at least ish comprehensible in case I need to debug into it - from what you're saying, everything has gone sufficiently well in terms of 'clean and robust' that that hasn't been an issue for you in practice ... but justified or not, it's going to worry me anyway.
Which programming languages do you have in mind?