It’s completely true that because RDS is a shared service, you may not have an RDS user that has the SUPER privileges upon the MySQL system schema(s), ‘mysql’ in particular, since with SUPER privileges on the system schemas you could potentially impact other RDS users’ service or access/damage their data. However, this in no way prevents you from granting ALL PRIVILEGES to a user that you create on a database that you have also created in your RDS instance. You simply cannot GRANT ALL PRIVILEGES ON *.* or GRANT ALL PRIVILEGES ON mysql.*.