Add body weight and the old gear sums to about three percent heavier than the modern gear. I'd say total weight matters more than gear weight alone, doesn't it?

I've done a lot of long hikes (200+km in the sahara, 6000+m mountains in kazakstan), and 2kg extra means a lot, like the difference between carrying extra fuel/food versus just clothing.

Anyway, you can try it yourself, wear a 2kg wax cotton jacket versus a 500gm technical jacket and see how you feel after a day's hiking.

Until you take your gear off, and it's in your pack. I'd much rather lose a kg of pack weight vs. a kg of body weight.