That's probably true. I've never used them in the US but they seem to often be the site of choice in Europe and Asia (and, based on one recent experience in Europe, can have inventory that can't be accessed any other way). That said, you also have to take direct bookings into account which is most of what I (at any rate) do.

You may have used them indirectly though due to them owning a lot of OTAs. It’s basically a duopoly of Booking Holding and Expedia Group.

And (South East) Asia

Under the brand name Agoda if I remember correctly