I would ask why should the Medicare Part B premiums work the way that they do? Medicare taxes are not capped so high earners paid a lot into the system to begin with compared to the average Joe and everyone gets the same Medicare benefits. So they paid more their entire working career for the same benefits. Then, to add insult to injury if one has saved and has high income in retirement then you pay more for the same benefits... again!
Why would we as society want to perpetuate such inequities?
BTW, I don't pay IRMMA but DM did after DF died.
To repeat one of your sentences, "Why would we as society want to perpetuate such inequities?"
Which inequities are you referring to, the income earned or the health care benefits?
Many people work 2-3 low paying jobs to make ends meet. Not everyone can have a high paying job. How much did you pay for childcare, lawn care, or housecleaning? Public school teachers are not highly paid, and private school teachers are paid even less. Do they deserve less health care in retirement?
The highest IRMAA brackets are a $487 surcharge for part B and $91 for part D, for MAGI over $500K for a single and $750K for a couple. With a $202 part B premium and $25 part D premium, the total is about 1.9% of a single person's income, leaving $490K for all other expenses. The average retirement income is about $60K-$90K, so the average single retiree pays 3.0-4.5% of their income in premiums, leaving $57K-87K for all other expenses. It seems the real inequity in the $413K-443K difference in money available for living expenses. Is there a different price for meat or milk or trash pickup or kW/hr of electricity based on income or NW? No.
A person earning $500K+ in retirement should not feel insulted or injured by having to pay more. Be grateful that you don't worry about affording food or gas or a roof over your head, and don't begrudge paying a few more dollars to keep the system solvent, unless you want to pay private health insurance premiums at age 85.
With great power comes great responsibility. In my opinion, the same can be said for great wealth.
With respect to the NW proposal, if one lives in a HCOL area, one can have a high NW based on the house you lived in. A 3 bedroom house in Sunnyvale, CA is valued at $1.5million+ whereas in Mississippi it might be $200K. Same house. A friend of ours is retired in Sunnyvale, in a house inherited from his parents in the 1990s, who bought it in the 1950s. He is still working part time and has a roommate; he was not a high earner. He might have a high NW, but it is mostly tied up in his house.