We arrived to find that the front entrance and stairwell were a construction site and that parts of the building were undergoing renovation. The apartment itself initially seemed fine, but then we discovered that the drains were blocked in both the shower and the kitchen sink - and after that, the power went out.
When we contacted the host, he replied that "Many buildings are being rehabilitated in Paris...." Next, construction workers entered the apartment with toolboxes and took apart some electrical components, leaving and returning with new supplies. They told us that the power would go back on at some point but would be turned off again the next day.
To all this, the host now replied, "unfortunately the building does not belong to me, I just have the apartment which belongs to me. power cuts only happen during the day and it was only there for a few hours. the installation of the new electric meter in the apartment lasts only a few minutes..." and so on.
We left the apartment, went to a hotel, and got in touch with the Airbnb Resolution Center. A representative responded very quickly, they looked into the situation, and we were issued a full refund for the rental amount, plus given a voucher to cover the service fee.
In response to our detailed complaint (with photos), the host had replied that the issues we raised "don't concern me." We'll leave it at that.
Thanks to Airbnb for taking care of us.