Disagree. Avro makes messages slightly smaller by removing tags, but it makes individual messages completely incomprehensible without the writer schema. For serializing data on disk it's fine and a reasonable tradeoff to save space, but for communication on the wire tagged formats allow for more flexibility on the receiver end.

The spec for evolving schemas is also full of ambiguity and relies on the canonical Java implementation. I've built an Avro decoder from scratch and some of the evolution behaviour is counter-intuitive.