Yeah, but it's a negligible rounding error of cpu time for each client.

Distributing this work ironically makes it much easier to centralize the authentication.

That's all clear to me. But technically there exists a method to revoke an issued token. It's just that long lived tokens mean potentially lots of them == increased storage cost. It would be pretty silly not to check for revocation. How would one implement logout otherwise? Relying on just clearing session cookies? What if I obtained those cookies using something else than a browser and I can hold on to the cookie jar? Not checking for revocation == doing it wrong.

The purpose of a refresh token to allow the app to short circuit the login process. Regardless of how long the token is issued for. It's perfectly okay to ignore refresh tokens altogether, if one wants to.