@Cronix How amount is a SAAS (Software as a service) system?
What are your thoughts on having an admin table for the system managers while users table for tenants (Different organizations subscribers admin users) and other users?
If you decide to build an extra table for the admins you then have to extend the default auth system which is a lot of extra work considering you could simply have a role and do $user->hasRole('admin') when needed.
Another option if you do not want to use roles nor a flag and need extra columns for your admins is to use a one to one relationship. Your admins table can have the user_id as well as the columns you need without messing with Laravel's auth system.