Every tone curve in any RGB space has a side effect on color saturation - period. Severity depends on many factors and sometimes we may even appreciate it for artistic reasons. For example, blackpoint setting (to the right) increases color saturation, mainly for the shadows with decreasing significance towards the lights.
Luminosity blending or changing to Lab-lightness (harmless at 16 bit/ch) can typically reduce such effects – but not necessarily. For example, increasing midtone brightness by means of the Levels’-“gamma” slider induces a broad de-saturation which isn’t much buffered by those measures.
Even, pure whitepoint settings are better done in normal RGB mode. In fact, this is the only exception with no side effect on color at all. Whereas Luminosity blending or Lab-lightness would lead to a de-saturation.
HSB could be an interesting option, however, color scientists don’t like it and PS doesn’t fully support it on an active basis.