It could be a useful feature as long as the feedback is anonymous. Unfortunately, companies running ranking systems have their own best interests in the forefront which causes issues.
Exactly, it's an incentive game. Airbnb has an incentive to maintain high rankings across the board, because customers compare ratings across platforms as if they're equivalent. If they see a majority of 3/5 on Airbnb, they're just going to go on Booking.com and book a 4.5/5 hotel instead.
The only way to avoid this I can imagine is relying on cryptographic zero-knowledge proofs to defer ratings to an external network (ideally decentralized, but a neutral third-party ala TripAdvisor could work too). The platform gives the customer and provider a token when the transaction takes place, and they can use it to anonymously sign a review on the external ratings platform.
