So, mostly, “the community” of people building on atproto are going to build things and then figure out what to adopt and use and interop.
The power imbalance is that the Bluesky team has funding and dedicated resources who are paid to work on protocol, as well as a large network where they can apply changes.
I’m looking for the proposal process https://github.com/bluesky-social/proposals to be open to all. “Who decides” is still going to be the issue 
There are the bits at the IETF, so over time the standards work will shift in a slower, more measured process there. Reading this previous post Web Standards and the Fall of the House of Iamus (Alex Russell) – standardization comes after usage. Running code and rough consensus is the input into the standards process.