On the topic of airstrips I think they should be moved under the aerodrome umbrella. Many authorities define aerodrome as anywhere aircraft can land and it makes little sense in separating one category from the others.
In that thread they speak of a lack of clarity, so I’ll give these possible definitions:
“Airfields” are aerodromes that although still a center of economic/leisure etc. activity have limited infrastructure compared to a proper aerodrome. Maybe they don’t have hangars, maintenance services, fuel, a paved runway, security, a barrier etc. but they still have some and aircraft can operate given restrictions.
“Airstrips” would be even less than that. They may be just an empty field where aircraft land. There are a lot of these all over the world especially in less developed regions.
As for differentiation, airstrips could just share the prop symbol. I’d actually say such informal aerodromes should have a further reduced symbol since they are very large in number and debatably in economic and social importance.