Filter knobs and polyphony don't play together well.
That's why they gravitate towards "leads" or "pads" over a separate bass or percussion track. Unlike normal Western polyphony you want the two to NOT form chords or counterpoint.
What is true in ambient is that you frequently do not want the third in the chords, because it makes the chords "too obvious". A lot of drone music involves a variety of chords with the third omitted.
What I mean is voice leading and counterpoint - once you have a filter sweep as an instrument you now need to deliberately avoid all that when composing.
People act as if these Western music theory concepts are grand universals, but they're really just useful conventions for the particular music instruments common at the time. They're not even universal for all of Western music; when the instruments evolved so did the conventions and the "theory".