The former being something entire countries are struggling with, how do we know the correct person is actually receiving the content, how can I be sure? WoT, PKI, whatever. You fail this, the rest is in practice IMHO less than useless. There's things like https://keybase.io that did try to solve this to a reasonable extent, PGP but more modern. It looked hopeful, but Zoom seems to only keep it on life support. Maybe someone will continue, anyways, I digress.
The second aspect is IMHO what determines how usable it is for a single person over long period of time. Maintaining backups of minisig keys, chat keys (or even not being able to do so), file encryption keys is difficult to say the least. It's unlikely you'll even be able to use a HSM for your secrets like a YubiKey. The same negatives listed against PGP apply to other systems suggested in the article. For example how do I communicate to people sending me encrypted messages that I lost and migrated to a new key/subkey? It's a very hairy problem.
(This reminds me, does anyone here know how to get PGP paper keys that use only english words e.g. "brunch pineapple house crow ..."? And does anyone know why we aren't using english words to compare PGP key IDs yet?)
I agree with a lot what the article lists, but the alternatives suggested really aren't compelling when looking at the actual problem. Judging based on the market share, I think I'm not the only one that thinks so.