Americans work like crazy don't take holidays...
No, not according to the available data. The United States doesn't even crack the top 10 within the OECD by this measure. According to the OECD, individuals who are employed in the U.S. work an average of 1,780 hours per year. #10 on the OECD list is Portugal (1,863 hours per year on average), and #1 is Mexico (2,257).
...and their entire paycheck goes in expenses and they will never be able to retire.
Again, the available data suggest otherwise. Let's look at two important numbers. First, the current (2019) average U.S. Social Security retirement benefit is US$1,461 per month. That's almost identical to what the future (age 65, Standard Plan)
Enhanced Retirement Sum CPF LIFE monthly benefit would be for somebody who has the ERS in his/her CPF Retirement Account at age 55 today, which is not very common in Singapore. Moreover, the U.S. benefit is adjusted annually for inflation, and the cost of living in the U.S. is generally lower. And there's a spousal benefit in U.S. Social Security which has no counterpart in CPF.
So that's the government sponsored system with practically universal participation (including legal residents), and it's comparatively more generous. Now let's look at private retirement savings. There are about 100 million Americans (out of a population of about 320 million, which includes children and young adults) who have 401(k)s and IRAs. The total value is US$7.5 trillion, a figure which has grown quite robustly over the years. The median account value for somebody age 65 today is a little over US$58,000. That's not a huge number, but it would easily add at least US$250/month to a retiree's income above Social Security. (That's assuming age 65 retirement and 20 years -- 240 months -- of drawdown. Also assuming zero income tax, but that's a pretty reasonable assumption at this level of total retirement income.)
If you also look at rates of poverty in the U.S., the elder cohort (age 65 and over) is comparatively doing well. That's not to say there's no elder poverty -- there is some -- but, as a cohort, senior Americans are doing well comparatively and historically.
I wonder if you call this developed and wealthy.
Yes, the data suggest those are fair descriptions of the United States. Wealth inequality is a significant and growing problem in the U.S., but that's true practically everywhere, including in Singapore.