No, not a monopoly. AirBnB is clearly a competitor in this space despite the various differences in targeted properties, and Google Maps also fills in this space.
You could call them rent-seeking middlemen, but not a monopoly.
You could call them rent-seeking middlemen, but not a monopoly.
Really? Huh.
I just looked at a dozen or two across Germany, France, Switzerland, Spain, Netherlands, Luxembourg, and Belgium, and while most had an option to book via booking.com (linked directly on the google search results) none had it as their only option, and they all had websites with direct booking forms of which only two were even styled slightly like booking.com
But I didn't actually try to book a stay at any of them, just looked at the websites, so if they redirect after that I would have missed it.