There is also index deduplication in Postgres 13 and the B-Tree enhancements in Postgres 12. All of these enhancements significantly improved the situation for workloads affected by what the blog post calls write amplification. (I myself call this phenomenon index version churn, since it is more descriptive and has less baggage.)

I was the author of all of the above, including the Postgres 14 work you mentioned (though Anastasia Lubennikova was the primary author of index deduplication). To me it feels like one very large project -- the effects are cumulative, and each major Postgres version had B-Tree work that built on the last release in one way or another.