it would be interesting if users shared their default shading settings in this thread

I took your settings, only made the default material brighter. I don't like the dark theme, because then Houdin's shading in the shadows merges the model with the background and it's completely unclear where the boundaries are. And for the dark gray theme, you need a brighter material for contrast.
if the background could be made darker than dark gray, but not black, it would be great. Maybe you know where this data is stored?

P.s.I would suggest that developers make such settings by default, it dramatically improves the legibility of the viewport. Now I stopped hating the Houdini viewport.