Friction shifters did get somewhat lighter over the years, as improvements to cables made lighter return springs practical. But I think the biggest difference is in expectations. Today's stuff is so light action that the older stuff feels way harder by comparisson.

I think back to the early days of mtn bikes using 6 speed thumb shifters. The action was so stiff, it wasn't that rare for folks to sprain their thumbs trying to downshift. The difference in feel of my current road bike and the Campy barcons on my '67 vintage Frejus is like the difference between my Miata, and some old truck without synchro. I road that bike for tens of thousands of miles, maybe that's why I have a strong grip.