Funny you should mention ASN.1. Protobuffers is Really just a toy ASN.1 written by some guys who just solved the problem at hand instead of looking further afar.
It's great for what it is. Many of us have written something similar.
It's not a pro level system designed by a serious telecom team.
I worked on LTE stuff during a research/engineering position. It was just 1 year and not my life's work, but I had to deeply understand ASN.1 for it, and I'd never heard of Google's Protobuf. I didn't like ASN.1 even for its intended use case. That big type system was far more complex than necessary for the protocols I was dealing with (surrounding the EPC mainly).
ASN.1 is more optimized in other ways that make sense, sacrificing some flexibility in favor of performance because the ends are expected to be more coordinated, but that's separate.
It's not a pro level system designed by a serious telecom team.