These concerns seem to be specific to cases where there are various competing high-level design "strategies" with political weight behind them.
There are cases where PG is missing high-level docs where I don't think this applies.
For example, there's no official doc on how to write PL/pgSQL code. There's just an extremely-low-level language reference, covering each syntax element separately. There's no cookbook (other than the few examples per syntax element that exist to document the edge-cases of use of that syntax element); no tutorial; no efficiency/performance/scalability guide discussing when certain language features should be favored over others given the current way they're executed (e.g. is IF-ELSE, CASE-WHEN, or a series of IFs with early returns cheaper? when should I favor using FOR with a query, vs. when should I query data into an in-memory array variable and then use FOREACH, vs. when should I query data into a TEMPORARY table and then query that?); no place where you can get a sense for how procedure CALLs interact with MVCC (e.g. when they acquire + release locks, and therefore how and when they cause blocking on contended tables vs. how and when a SELECTed function that uses dblink/fdw to run independent txs would do so); etc. There isn't even a single mention of which PL/pgSQL exceptions are potentially raised by what PG builtin functions when called in a PL/pgSQL context; how to name those exceptions to match on them to catch them; or how to raise them yourself. I often need to dig into the PG source code to figure that out! (PL/pgSQL honestly feels, in docs terms, like a proprietary third-party language-engine "plugin" that someone bolted on, where the docs were expected to be provided by the third party, but never were. But it's not! It's a first-party language, and the reference implementation of how to create a language extension!)
There are cases where PG is missing high-level docs where I don't think this applies.
For example, there's no official doc on how to write PL/pgSQL code. There's just an extremely-low-level language reference, covering each syntax element separately. There's no cookbook (other than the few examples per syntax element that exist to document the edge-cases of use of that syntax element); no tutorial; no efficiency/performance/scalability guide discussing when certain language features should be favored over others given the current way they're executed (e.g. is IF-ELSE, CASE-WHEN, or a series of IFs with early returns cheaper? when should I favor using FOR with a query, vs. when should I query data into an in-memory array variable and then use FOREACH, vs. when should I query data into a TEMPORARY table and then query that?); no place where you can get a sense for how procedure CALLs interact with MVCC (e.g. when they acquire + release locks, and therefore how and when they cause blocking on contended tables vs. how and when a SELECTed function that uses dblink/fdw to run independent txs would do so); etc. There isn't even a single mention of which PL/pgSQL exceptions are potentially raised by what PG builtin functions when called in a PL/pgSQL context; how to name those exceptions to match on them to catch them; or how to raise them yourself. I often need to dig into the PG source code to figure that out! (PL/pgSQL honestly feels, in docs terms, like a proprietary third-party language-engine "plugin" that someone bolted on, where the docs were expected to be provided by the third party, but never were. But it's not! It's a first-party language, and the reference implementation of how to create a language extension!)