1973 bumpers: significantly lighter than '74+?

I have been plotting to order up fiberglass front bumper for the Dart for a while now...I kept hearing how much weight there was to save off of the late A-Body cars because the bumpers had the extra support built in and weighed a lot because of it.

Honestly, despite having climbed all over this car for the past two+ decades, I never gave the bumpers much thought but when I was hitting the bolts with some penetrating oil in prep for removing them down the road, they didn't look as I was led to believe. There didn't seem to be some massive chunk o' steel back there at all.

Sure, the bumpers are made from pretty heavy gauge sheet metal but could it be that there isn't as much weight to save on the '73s than there are on later cars?