Fair points on why Iron Man hasn't really caught on that much aside from Robert Downey, Jr.'s (iconic) portrayal of him, especially bringing up his connection to the military-industrial complex. A similar argument could be made of Captain America in terms of him starting off as a propaganda tool to get America and Americans to join World War II and fight the Axis Powers, but the comics (and related media) have gone a long way to distance him from that by having the character and his stories interrogate and challenge the more morally corrupt and/or otherwise suspect aspects of American government and institutions, so he's not exactly a simple puppet or avatar for American militarism anymore. In that same vein, going back to Iron Man as a character and a concept, given how great wealth in modern society is increasingly interrogated and challenged, if not flat-out condemned, as a driver and/or product of moral corruption and deep-seated social inequity, it's rather difficult nowadays to cast him as a completely, unambiguously heroic figure.