Relative and absolute deprivation have absolutely little to do with how the poor feel in the US. Further, your argument basically boils down to "people used to be in concentration camps and you're not, you don't get to be upset."

Being content and happy in life has a LOT to do with expectations and we've done a great job of promoting huge expectations for Americans ala "The American Dream!" Poor people don't care that Bill Gates and Elon Musk have near unfathomable wealth. They care that a lifetime of hard work doesn't guarantee a decent home, access to affordable healthcare, or the security to live without constant threat of basic necessities being out of reach.

Further, the poor should demand more! All we hear from the upper class/business owners is more, more, more! Get leaner, cheaper, and make more money! The poor are only following the examples set by the "titans of industry." And if they didn't constantly ask for more, they would be in even worse shape than they are now.

And finally, if you ever want to convince others of your viewpoint, comparing America to third world countries is not the way to go. You've got to put on your oxygen mask before you help those around you. Otherwise you all end up screwed.