#1 on the list is Walmart, which has a similarly low on-paper 2-3% profit margin, but I don't think anyone is deluded into thinking the company, the Waltons, or its investors are barely scraping by.
#2 is Amazon. Again, low profit margin. Again, plenty of profit.
Nobody is arguing that you can't buy a luxury yacht or whatever with UNH's profits. It's pretty obvious from the original comment[1] is the argument is that even if all the profits were plowed back into approving more claims, that it would only only increase the approval rate by 5-6%, which is a totally minor amount.
Walmart is amazingly efficient and basically the case for how economies of scale benefit the consumer. If you broke it up, prices would go up, not down.
Walton's do great because of the scale, but is a very lean and efficient organization. Take them entirely out of the picture and the consumer would hardly notice.
Even if you look at the company as a whole, there aren't much profits to go around.