AWS RDS : Setting Create and other grants only for single Database is not working
RDS only allows you to grant privileges on the schemas you create. System level schemas are blocked as the “master” user only has certain privileges with the with grant option.

That being said the usual statements of GRANT ALL PRIVILEGES and *.* don’t work. You have to grant privileges explicitly by schema to a user and those grants can only be at most the same ones you have as the “master” user. 

This article is for creating another “master” user and you can use it as a reference to model the permissions you are trying to setup by removing the privileges you don’t want the user to have. 

Additional Master User in AWS RDS