Yup - OIDC can be boiled down to:

1. The OG OAuth2 spec never said anything about identifying principals 2. OIDC mandated an id_token to avoid the hit of POSTing the access token to an introspection endpoint 3. The shape of the id_token is a JWT

This doc is junk, btw - it's suggesting the client use the id_token for the purposes of authentication? I wouldn't trust that token beyond some basics, unless you have very strong controls over the authorization server and IdP to ensure things like email verification are propagated correctly.