Hmm, on second thought, I guess you're right. Now that I reflect on it, I remember that there was some controversy among the fans about TMP being saddled with a G rating, since it gave the impression that Paramount wasn't taking the film seriously enough. I'm surprised I forgot that.
Still, as discussed above, even in the late '70s there were still G-rated films with content that would never get in a G-rated film today, like Sinbad and the Eye of the Tiger
. So the G rating was at least still somewhat broader then than it is today.