The USA can use money as a lever to seek more control and accountability from the WHO. A Chinese delegate (Margaret Chan) was director of the WHO from 2006 to 2017, and after her, China has sought to keep as much influence through the new director.
France found it's earliest case of Covid-19 from November 2019 DNA sample archives, one month before the Chinese started reporting the illness, so there are arguments about the WHO's efficiency in China, and the undetectable rise of Covid-19 is being used as a tool for accusation of the WHO. That accusation is fomented by the WHO's lack of urgency in the declaration of a pandemic.
The WHO is also degraded by money, (it spends more on executive travel than on health) business class last minute flights, five star hotels, and WHO executives are good targets for bribes. The American government is also degraded by businesses, career politicians and money and they want to reduce frictional foreign influence of the WHO.
The USA and the EU have very little leverage over the accountability of the WHO, because it governs itself and elects and appoints it's own staff.
A 2 billion pound organization, which has millions of dollars of contracts in countries where money is very difficult to trace, the WHO would benefit from reform. That is one possible benefit of suspending funding.
Sometimes, organizations that govern pharmacy and health regulation authorities can become so corrupted with time, it is best to gut them of all their operatives and replace them with a modernized organization which does it's job safely. That happened in the UK when Blair completely dismantled the pharmacy and health regulation safety authority and built a new one which actually did it's job.
There is less long term strategy in USA foreign policy. "short term-ism" is the defining theme of US foreign policy according to a Cambridge friend who is an Asian current affairs analyst. The WHO decision may be like the Paris Agreement, which benefits a US special interest (its fossil fuel industry) in the short term, and impoverishes the US economy in the long term.