The US is never going to realize diminishing returns. There is fundamental differences between sanctions by China and sanctions by the US. Sanctions by China are only enforced in China, by China so anyone can easily evade them by not visiting China and not directly doing business with China alone. In contrast, sanctions by the US are not only enforced within the US territories, but also in its countless vassals all around the world. Moreover, the US military and agency are actively enforcing its laws (by kidnapping people and seizing ships and airplanes etc.) on international waters/airspaces. Even Chinese companies in China are afraid of US sanctions and obey them.
Not doing business with China, or interacting with chinese products/services/advertising is going to become pretty tricky.
For example, could China have Pompeo fired from Fox by pulling adverts from Chinese companies? If you think no, then also consider the amount of Chinese shareholders in companies that advertise.
Maybe China doesn’t have enough ad spend yet to use this power, but it’s clearly increasing, they dominated Euro 2020 for example. Every advertisement hoarding was form Chinese products almost. 100” laser tv anyone?
It would be super interesting to know how much of Murdoch‘s revenue comes from China wholly or partially owned companies.