So based on reading your other responses your complaint is that "I think RFCs are built on practice than the other way around" which doesn't mean much, considering that's what is happening! They are building on practice. Most if not all RFCs anywhere, including the IETF, actually see lots of revisions, and QUIC is hardly very different, and there is no hard rule about how standards are formed. This is how it works.

EDIT: I was too rude/curt and re-edited this. Sorry.