Resolving complaints after check-out is challenging and less likely to result in compensation. In the future, communicate any complaints to the property during your stay, so the staff can ensure the rest of your stay is comfortable.
My reply was: ok, there are choices. I switched to Google Maps, check reviews there, and prefer booking directly on the hotel/owner sites.
I had a brief stint working for a hotel booking competitor and, sometimes, a transaction would go through 3-4 hands, each taking commission, before reaching the hotel and I just hated that.
This spring we wound up stranded in Amsterdam for an evening and I needed to book a hotel fast. I checked booking.com and saw what was still available at the moment and I found a hotel - a double room on booking.com was 230EUR. I call the hotel, I tell them I want to book a room for tonight, total number of people etc. The receptionist comes back and tells me a double room is 285EUR. Do I want it? I do not. I went back to booking.com and reserved the room there.
I can also say that I had a problem with a dishonest property description (regarding parking) and complaining to Booking made them produce an underground parking space in 5 minutes - albeit this was before checking in.
Bcom and other OTAs negotiate discounted rates on your behalf, because they bring in so much volume they can pressure the suppliers. Similar to how Walmart gets rock bottom prices on goods.
Sometimes it's cheaper to directly contact, but often it is not.