Sometimes chromatic progressions seem to just shift a chord a certain amount of semi-tones with no regards to the scale like chromatic mediants and chromatic planing, chromatic alterations, etc. But other ones seem to have more scale reasoning behind them like leading-tone chords, modal mixtures, secondary dominants. Is there a distinction between these two groups or are they all just considered chromatic progressions?
I think you laid out several good categories in your question.
You might consider some kind of contrapuntal category. That is what the chromatic augmented sixth chords really are. Chromatically altered subdominant chords to get the characteristic half step contrapuntal movement in contrary motion.
Passing motion seems to be another way to introduce chromatic chord. "Block chord" style inserts diminished seventh chords between diatonic chords. You could view that as a kind of leading tone chord, but the passing motion aspect seems cast the diminished seventh as a decorative element. The descending chromatic chords in Chopin's
E minor prelude also use a kind of passing motion dropping by half step to various diatonic tones until it gets to the dominant.
I hesitate to give a specific number of categories, but I think you should look for more than two. At the very least I would not put leading tone chords and borrowed chords into the same category. One tonicizes while the other does not. That's is a huge categorical difference!
Just on face value, it might actually be a more useful analysis to scrap the idea of two distinct categories and instead conceive a continuum running from nearly diatonic to pure chromaticism. One could then sort of place individual chords somewhere on that scale; As an example, I'd say modal mixture is a lot closer to the "chromaticism" end of the spectrum than the more functional end of the spectrum, at least when compared to secondary dominants.
And just as certain sets of notes can have different meanings in different contexts, there will be a large amount of variation within any certain type of non-diatonic chord or tonality. I still think the existing categories of non-diatonic chord usages are valid and useful, but I think it's also quite important for the analyst to be conscious of a non-discrete continuum of functionality.