I lament to say on this matter, I do not have words of comfort or support to offer.
With all due respect, in my honest opinion, if one are in the accommodation business, one have to deal successfully with the early checkin and late checkout expectation.
It is part of the business.
Yes, Airbnb is not a hotel, but it is part of the accommodation business sector.
Most of the hotels, from the cheapest to the most expensive have a room (or same space) available to store guest's lugage when they have to leave the place after checkout time or when they arrive before checkin time.
Many hotels let the guests have early checkin when there is availability.
From the guest perspective, it is not an absurd to expect an early checkin when there is availability or to ask to store their lugage when they have to check out long before their flight time.
There are not perfect guests that always arrive in a city in a pefect time for checkin and that find a perfect flight that better suits checkout time. The world is not perfect, everything in the world is more complicated than easy.
In my honest opinion, if the host are having frequent problems with late checkout and early checkin, there are 3 alternatives on what the host have to do:
1- Give up hosting
2- Find a solution instead of complaining about guests. Do what hotels do, arrange some place to store lugage.
3- Change your policies and prices. Raise the nightly rate and block one day before and one day after each stay.
By doing that (2 or 3) the host may have happy guests, less stress and probably better reviews.
Just my honest opinion.