One factor I was thinking about in estimating US fatality rates based on data from China, beyond the Chinese data being mostly nonsense, is that the US has a higher percentage of 70+ year olds than China. In the 80-84 range, for example, they are 1.1% of China's population and 1.9% of the US population. That factor alone will increase the CFR in the US, independent of all other considerations. There are 22.7 million Americans in the 70-79 range and 12.7 million are 80+.
The older age groups are also more likely to get a serious form of the illness, although I have not seen an estimate on that. But if 80+ year old persons with a serious form of the disease are ~50x more likely to die from it than younger adults, they are probably many times more likely to get a serious case of the disease. One commonly cited estimate is that 80% of people who are infected get a mild form of the disease, but that will not be true for older age ranges.
Older people in the two countries may also have vastly different living arrangements and social activities with vastly different risks of infections. Consequently the CFR among those with a serious form of the disease could be significantly higher in the US. It would be nice if we had some trustworthy data to work from.