This also lets you use your shell's tab completion or even a fuzzy finder to list and select identities.
But perhaps age is better suited as a backend in other apps, especially Go apps. A good feature of PIV applet of Yubikey 5 is that it stores 24 keys. compared to 3 in OpenPGP (although any app including GPG could make use of those 24 slots).
What I am looking for these days is a back up tool that uses age. Can an app like restic use age as backend?
Note that not all 24 of those keys are suitable for age usage. The 4 main keys have specific usage definitions in the PIV specification that mean hardware tokens alter how those key slots behave. Only one of them (the KeyManagement slot) has a definition that allows encryption, and even that I was somewhat suspicious of overlapping with, as I couldn't predict how those existing keys were being used, and didn't want to support every possible key type that might be in that slot (which users likely wouldn't be able to alter).
age-plugin-yubikey avoids this complexity by only interacting with the 20 "retired" slots, which have no constraining definitions. (I am considering adding restricted support for the KeyManagement slot specifically for CAC card users who aren't allowed to add new keys to their cards [0], but this would be behind a default-off feature flag to keep the primary UX simple.)
A PGP keyring is a list of identities. Once you have verified an identity you can not be tricked into using the wrong encryption key for that entity. You can then be sure of the authenticity of any messages/files you get from that entity.
I get that it's out of scope and wouldn't be that hard at all to implement a wrapper that handles this, but without that functionality I find it much less enticing because I'm left to think about something that the other tool I use handles (and as you've noted, a lot more seriously too).