I'm primarily a software engineer, not a member of "large support teams". I've also worked for many years as an independent consultant, brought in when things go wrong, certainly not when they were first "installed". I'm not "afraid" of anything concerning my knowledge going "out the window". If MySQL suddenly disappeared worldwide, I could happily pivot to some other area of software engineering, or I could simply retire. Please stop make assumptions about other people who you know nothing about.

I'm responding to you because you're repeatedly posting factually incorrect items, for years. For example you and I have directly discussed the "MySQL doesn't use SemVer" thing before on HN, and yet here you are again in this thread, claiming 5.6 to 5.7 should be a "minor" upgrade.

Anyway, to the topic at hand, as others have also mentioned in this thread: historically the difficulty with Postgres upgrades has been the lack of cross-version replication, due to Postgres WAL replication being a low-level physical replication system. This made it difficult to perform an upgrade while keeping your site fully online. Perhaps the newer logical replication support makes this easier these days. I hope to learn more about it someday. If you can share your process for upgrading a Postgres cluster while keeping it online, that would be helpful and informative.