> This leads to authors having to re-explain their thinking in detail

What I like about RFCs (or similar documents) is the ways they work to prevent this. Recently I was involved in planning an initiative without a document like this, and we had to keep explaining and re-explaining the motivation for our decisions to stakeholders and higher-ups. With a document (assuming everyone reads the document before giving feedback), most questions get pre-empted; the ones that don't only need to be addressed once, because the answers end up in the version of the doc which you show to the next person.

Certainly I think it's worth being selective about who you're soliciting comments from, to avoid a too-many-cooks situation, but rare is the project that doesn't need anyone's approval or feedback. Presenting a big fat document gives a sense for the amount of thought that has gone into the design, which quells the kind of off-the-cuff "why not X?" comment you might get in response to a boxes-and-arrows chart and a high-level summary.