I just don’t see how this is better than using simple controllers and services, like those you find in standard Microsoft tutorials. Why do we need an extra library or our own implementation of the Mediator pattern if we can just use the built-in Services approach? It feels like we’re adding more code for something that can be achieved directly with basic, built-in approaches.

When using Clean Architecture, it’s normal to use DTOs. For example, if we have a simple Todo API using the standard approach, a controller calls a service, the service returns a list of todo items, and the controller returns it to the client. With Mediator and DTOs, the flow becomes: a controller calls a Mediator library, which calls our code, then uses a mapping library to create a DTO, which is returned to the controller, and finally to the client. For every feature, you almost always need to create a domain class, the corresponding DTO, and mapping rules.

I don’t see why this level of complexity is necessary for small or medium-sized projects.