Those are called opaque rates in the business, but not comparable to being able to reserve a hotel room directly via a website for less than the hotel’s own website.

It does mean when people/hotels say “you’ll get the lowest/best rates direct so don’t use an OTA”, that’s a lie/not exactly true.

They don’t like it when you book through a travel agent, but they really have a love/hate opinion when you book an express/mystery deal

A reasonable context of “you’ll get the lowest/best rates direct so don’t use an OTA” is reserving a specific type of room at a specific hotel at a specific time.

It is unusual to be willing to gamble on which hotel one is reserving in exchange for an uncertain amount of savings.

They usually publish what the discount is, but yes, there is uncertainty in which hotel you’re getting.