OK but that still doesn't eliminate the spores floating in the air. If there are enough spores in the soil to affect the plant there will be spores in the air. How does a different grow system or style prevent that? Maybe I'm not understanding so you may need to break it down into simpler terms.
it eliminates a singular source. you are correct in it is primarily airborne. it lives on plant leaves, if none are available it will drop and lie dormant in soil until conditions are correct for it to emerge. a lot of organisms survive that way.
there would be no pm here in summer otherwise. it can't survive the winter temps unless it embeds and goes dormant. same with larger organisms outdoor like spider mites as well.