The ideas that I as a civilian was sold over the past decades don't appear to hold up any longer.
As someone a while back put it, Russia lost several Bundeswehrs worth of equipment and keeps on grinding. Neither side is able to mass large forces, in a large part due to drones. And Iran can punish the US despite being comically outgunned.
Modern equivalents of Sherman and T-34 tanks over burdensome Tigers and a population willing to support heavy losses.
While Iran has faired better than I expected, it's a reach to say they've punished the US. The US losses are comically small. Of course wars aren't won solely based on battles...
A Bundeswehr worth of equipment is so little nowadays that Bundeswehr itself lost several Bundeswehrs worth of equipment while being at peace for the last few decades.