The reason we have this is because:

1. We hooked up Shib for Marist so their users could log in before we had any user import functionality
2. Marist's Shib didn't give user metadata, so they all resulted in externalIds as the user id
3. We developed user import, and because of the old users already signing in, we wanted to not wipe out their display names, so we created this one-off rule to make it work

Now that we already have user import (and in hopefully many cases Shib can provide user metadata), it seems unlikely that this workflow will happen this way again. In which case this `externalId === displayName` check is legacy and probably not worth having laying around incurring technical debt.

Is that the case? /cc @nicolaasmatthijs