Hi David,
Thanks for contacting Syncfusion support.
Express makes developers easy to do tasks from building a REST API to building routes for simple web application by using route parameters and query strings as it has a powerful routing API, whereas in asp.net core developer can develop a web application without any additional frameworks or libraries, as the .net framework contains everything a developer needs, but the language and framework were closed-secure, and ecosystem was Microsoft-oriented.
Please get back to us if you need any assistance.
Regards,
Muthukumar K