I disagree. The USMC doctrine on this matter has remained the same for generations, so that doesn't explain the increasing loadout. Also, and I don't know what the official Army guidance is on matter, but we took over an AO where an Army unit had previously been responsible. They regularly got ambushed, and regularly broke contact.
One development that I heard about a couple of years ago, which should certainly ease the burden, is that the Corps dropped the M249 in favor of a heavy barrelled M16. That is a lot less weight, considering how every fireteam had previously been equipped with a belt fed machinegun (5.56, but still).