> security under a hostile setting

Yes, but security usually includes availability, and I mentioned a setting with service blocking above. Like that by a government.

> (Centralization itself is a red herring. One may as well claim that PGP is centralized, given that there’s only one prominent keyserver still limping around the Internet.)

How is it a red herring?

> For messaging/secure communication, use Signal. It’s open source.

From my point of view, it is complicated by Signal being blocked here (and it being centralized helped to establish such blocking easily), likely the phone number verification won't work here, it is not available without a phone, and it is not available from F-Droid repositories on top of that. Currently money transfers are also complicated, so finding some foreign service that would help to circumvent phone number verification is also complicated, and not something I would normally do even without that. All this Internet blocking is a new development here, but such availability issues due to centralization were anticipated for a long time, and are a major motivation behind federated or distributed systems. Some mail servers are also being blocked, but generally mail still works, and less of a pain to use.

> For file encryption, use age. It’s open source and has multiple mature implementations by well-regarded cryptographic engineers.

> For signing, use minisign, or Sigstore, or even ssh signing. All are open source.

These I find to be okay. Having to install them in addition to GnuPG that is usually already available, but that is to be expected; they are available at least from Debian repositories, so not something to complain about when considering alternatives. Likewise with the key sharing: not getting to reuse OpenPGP's PKI, and will have to replace that somehow, but it is not like it is used widely and consistently anyway, so perhaps not much of a loss in practice. Likewise with familiarity of the users: I would expect a little more friction with such tools, compared to GnuPG, but not much more. And I don't see actual usage downsides apart from those. Though the benefits also seem a bit uncertain, but generally that sounds like a switch that makes sense to consider.