Right. The de facto/apparent case that many users encounter shouldn't be considered the correct mental model or implementation pattern... it just explains why some people see it that way.
Not long ago I designed an authentication system which had to be disconnected from authorization pretty fully. The authentication was global in a multi-tenanted system, but access to any tenant was authorized at the tenant level (as well as all other authorization concerns). To be fair, there was some global authorization concerns, but the vast majority of authorizing actions, including tenant access was governed at the tenant level after authentication.
Not long ago I designed an authentication system which had to be disconnected from authorization pretty fully. The authentication was global in a multi-tenanted system, but access to any tenant was authorized at the tenant level (as well as all other authorization concerns). To be fair, there was some global authorization concerns, but the vast majority of authorizing actions, including tenant access was governed at the tenant level after authentication.