another bytecode interpreter ?

While ASN.1 *is* riddled by some design-by-commitee issues that make the grammar hard to master and the implementations rare and buggy, it remains supperior in flexibility, features and packet size. As with any tool, it's not a one-size-fits-all, but there are a lot of areas where it is a winner.

Concerning CPU usage, while hard to compare (the codec gives you many data verifications for free, which you have to write yourself with the likes of protobuf and msgpack), it is nothing to be ashamed of. And while some people have 10Gbits to play with, others are more concerned with the per-MB data roaming fee that is drilling a hole through their wallet.