You are right. When you are using the Amplify Framework (libraries, CLI, UI components), you're using other AWS services like Amazon Cognito for authentication and identity, AWS AppSync for GraphQL APIs, Amazon DynamoDB for NoSQL database.
Because AWS Amplify leverages AWS services underneath, it's built for scale on day one. You'll get access to a broad selection of services with deep functionality and be able to adjust as your needs change. AWS Amplify also offers an end-to-end solution for the development workflow of your app, with continuous workflows and feature branch deployments.