I think there's a potentially big advantage to having a 3rd party involved. It can help arbitrate when there are problems. However, the OTA must really help both parties, and resolve any disputes, instead of washing their hands off it and saying they're just a messenger confirming the booking. There's little value in an OTA that only provides booking confirmation and that's it.

As far as I'm aware airbnb has made a lot of progress in this very area, verifying photos and information posted, checking the identities of the guests, that helps protecting both the host and the guest. There's no reason why OTAs can't do the same with hotels.