I agree that things have changed. I started 3 years ago and the place needed work and even so, I would get 5 star reviews because the rating system was explained well to the guests and I mentioned that my place is a work in progress. I also do not think it is up to the hosts to explain the rating system because it would seem we are fishing for good ratings. I got 2 ratings of 3 stars recently within 2 weeks and although I had 3 ratings of 3 stars in the past (over a 3 year period with almost 300 reservations now), it was a long time ago, the place has been massively improved, and it seems like what you are saying is true, i.e., the new rating system is not well explained and way too long and confusing.
The guests have changed too, I used to get full explanations of why they are coming, etc, now it's just "coming to see redwoods." I check in with a note to all guests when they arrive and they used to get back to me telling me that things are well or if they had a request. Now, no answer at all. Could be the way they advertise now, as in the past it was "Live like a local," and now it's more like "Sip wine off the balcony of your castle overlooking the Mediterranean." So yes, it really can be very frustrating.
There are other things too, like I don't allow children under 12, yet in the last month I have had 2 guests that arrived with kids under 12. I think airbnb should help it's hosts out a lot more by telling guests to read everything and be respectful because they are, indeed, coming onto a person's personal property and it is kind of a big thing... They should also explain the rating system, and they should require clear photos and full info from every guest. I really am surprised and upset that they do not do all when a new guest signs up.