I completely agree. Guests don't understand exactly what the stars mean, guests don't understand that a '4' is a fail in Airbnb's eyes and Airbnb don't understand that some guests will never give 5 stars, no matter what; or if they do, they choose to ignore this inconvenient truth.
It pisses me off mightily when, as happened to me recently, a glowing review that waxes lyrical over every aspect of the guest's stay is accompanied by 4 stars in every category right across the board.
I think Airbnb needs to be proactive in three key areas. Firstly, they need to educate guests that 5 stars is expected unless there is an underdelivery of the offering.
Secondly, they need to make sure all guests are on the same page as to what the individual stars are actually measuring, eg. what does 'Arrival' even mean?
Thirdly, when a guest gives less than 5 stars, the guest must be asked to explain why.
The only aspect of the stay that is subjective is 'Overall Experience', the rest is objectively verifiable and therefore guests should be asked to explain in what way the listing deviated from the offering in terms of Location, Accuracy, Value, Communication and Arrival.
I explain every aspect of my listing in mind-numbing detail, include dozens of photos and even include a floorplan that is accurate down to the placement of lamps and vases. There is no way a reasonable person should give me less than 5 for the 'Accuracy' metric, yet they do and can and it goes unchallenged.
I had one guest who famously began his review with the words ...."The most important thing for me to note is that this is not your typical "entire home/apt" listing. This is clearly described in the description, but I did not read it so I was surprised when I arrived." And yep, gave me 3 stars in Accuracy.
It's just so wrong to let this stupidity go unchallenged.