No you are still misreading the point. The complaint isn't that something like crypto_aead_chacha20poly1305 exists. It's that encrypt_message_symmetrically doesn't exist in most places.
It's perfectly imaginable for a library to exist that is designed for a specific use case (eg securely send a message to a recipient that already knows the key), is implemented across many languages and platforms, and defaults to the same algorithms and settings on all those platforms.
It's also perfectly imaginable for such a library to evolve over time, as insights in the security community improve. Eg it could add support for more algorithms, change defaults, etc. And it could provide helpful tools for long-time users to migrate from one algorithm/setting to another with backward compatibility.
It's hard to do, sure. But it rubs me the wrong way that the same people who keep repeating "don't roll your own crypto!" make it so needlessly hard for non-crypto people to use their work.
I think libsodium comes close to this ideal, but I still feel like it's pretty hard to navigate, and it mixes "intended for noobs" with "know what you're doing" functions in a single big bag. In a way, JWT is another thing that comes close, if only it was more opinionated about algorithms and defaults. Paseto (a JWT contender that, afaik, never made the splash I'd hoped it would) seems great, and I guess my entire rant boils down to "why doesn't something like Paseto exist for every common security use case?"
