> This insane list of restrictions is the result of unprincipled design choices and bolting on features after the fact

I'm not very upset that protobuf evolved to be slightly more ergonomic. Bolting on features after you build the prototype is how you improve things.

Unfortunately, they really did design themselves into a corner (not unlike python 2). Again, I can't be too upset. They didn't have the benefit of hindsight or other high performance libraries that we have today.