Creating a framework is the correct path.

• It allows you not to re-code everything needed to create a window every time you start a project.
• It allows you to build an organized set of code you can easily move to the next project.
• It eventually allows you to port your engine to another platform or API, such as to VULKAN, Direct3D 12, Metal, etc.
• It allows you the possibility to improve performance (though just building a framework in itself doesn’t necessarily give you any gains or losses in performance—you have to code performance into your framework).

Slamming everything into a single file is just for the sake of making the tutorials easier to follow. Outside of that, it is extremely bad practice.

L. Spiro

In UE4 the RHI is a low-level graphics API designed by Epic and implemented via platform gfx APIs (D3D, OGL, Metal, etc.). RHI - quite - removes the need of writing different render path/different framework implementation, however capability differences of different platforms and different gfx API still take place (mostly exactly in RHI implementations). It's mostly a different design choice.

Since most of current gfx API still have a lot of abstraction, the RHI approach could turn into a double-edged sword, especially for unexperienced developers, resulting in awkward design and higher overhead.

Yes, all but RHI is an API based on the concept of command lists, to draw a triangle you will call FRHICommandDrawPrimitive::Execute instead of ID3D11DeviceContext::Draw.