Preferred datasource for Report server to secure data

Hello Community,

In order to secure data in an organization , what kind of datasource should we prefer to use : cubes SSAS, datamarts? or is it secure to let report developers accessing direct databases (relational ones)?

we are thinking of restricitng access to direct relational databses so we are suggesing to create a layer between power bi report server and databases ones . This layer should handle server for cube ssa or datalakes. Should this be a good idea? 

It is easier for developers to access the DB directly but in matter of securing data we are proposing this idea..

Any help will be appreciated

thanks