For a client implementing CRM Analytics with a variety of user roles, creating and assigning Salesforce permission sets is the most flexible and scalable solution. Here's why:
Flexibility and Customization: Permission sets allow for specific access rights to be compiled and assigned based on user roles without altering their existing profiles.
Scalability: As the organization grows or roles change, permission sets can be easily adjusted or reassigned to accommodate new requirements or users.
Simplified Management: Managing access via permission sets simplifies the administration of user rights, making it easier to ensure that each group has the appropriate level of access.

https://trailhead.salesforce.com/en/content/learn/modules/analytics-app-design/principles-good-design

The issue with the security predicate not functioning as expected likely stems from a permissions issue related to the custom field Demographic__c on the User object. Here's a detailed explanation:
Field-Level Security: If the sales reps do not have access to the Demographic__c field, the security predicate which references this field cannot execute properly as the system cannot evaluate the predicate without accessing the field.
Permission Settings: Ensuring that the sales reps have the necessary permissions to view and use the Demographic__c field is crucial for the security predicate to function correctly.
Data Visibility: The security model in CRM Analytics relies heavily on the underlying data permissions in Salesforce. If these permissions are not correctly configured, the expected data visibility through CRM Analytics will not be achieved.