If we include stay-at-home parents and people taking care of their parents, then China's GDP is way more underestimated, since in Chinese culture people tend to look after their family even more.
If one goes by IMF's definition of GDP as "GDP measures the monetary value of final goods and services—that are bought by the final user—produced in a country in a given period of time (say a quarter or a year).", then yes the U.S. is overestimating its GDP by including imputations, because homeowners don't buy their own home every month as a rental service. And why stops at imputed rents? Let's also include stay-at-home parents and people taking care of their aging parents.