As you mentioned, you are moving to SAP so it means you are moving to SAP HANA Cloud platform or backend SAP system. You can continue with just HTML Angular application that can connect to the backend via an OData service.
Following are the advantages/disadvantages of using angular framework:
Using Angular, you can develop complex High interactive rich internet web application.
Angular application can be easily integrated with third-party library like Kendo UI
You can easily manage the state of the UI objects and control over it
You can easily perform Unit Testing
You can also refer to this link for more details about SAP UI5 vs Angular framework −