I'm not sure why you are trying to look away from the fact Affinity Photo is an image editor AND a RAW developer. Just like I don't use Lightroom, I use Photoshop and ACR.
When Affinity develops a raw file the raw file is not destroyed - this is obvious, the raw developer is not destructive. The settings used to develop the raw could be saved within a sidecar file without any problems or length coding. The settings are not an 'image file' they don't need to be another image format, they are just a text file - this is obvious. I presume you know what an .xmp file is - it's not an image file. I can't believe I'm having to explain this.
The raw develop settings, under the Basic, Lens, Curves and Tones tabs, can at present be individually saved as presets - these preset are not image files, they are just text files - this is obvious. If all the Basic, Lens, Curves and Tones tabs could be saved as one collective preset then associated with the raw file as a sidecar then the raw developer within Affinity would become incredibly useful - and just by saving presets collectively as a sidecar. Affinity already has all the raw power it needs, it can save presets, it just need the guys at Affinity to do an afternoon of coding to add the sidecar save/load ability.
Alternatively we could all forget that Affinity can already develop raw files and save raw setting presets, and also pretend that it destroys raw files.