In this context it clearly is - if the server assumes the request sent by the client is always untrusted, then any capable device / app can use the service and

In this context it clearly is - if the server assumes the request sent by the client is always untrusted, then any capable device / app can use the service and it's possible to manufacture that device / app without permission from some company that has a dominant market position.. I acknowledge though, that this is incompatible with many practical scenarios, and CPC advertisements are one of those. It's hard for me to argue here theoretically without taking context into account, as it turns out what I'm arguing for depends on it heavily.. It could be possible for Google to make changes where while theoretically possible to compete, it's not practical, and when it gets practical, Google could make another change and so on..