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.

No. Weight x distance from center of mass is the real metric of burden.

Carrying your lunch on a 10-foot pole, keeping it off the ground at all times, versus slipping it into a fanny pack - or eating it and carrying it in your very center of mass.

I noticed while ultralight hiking (full kit without food, fuel, and water under 9 lbs, for multi-day excursions) that how close your backpack was to your back mattered. Unfortunately, if it was tight to your back it overheated you, so a standoff of an inch or so was essential. I considered dividing it front and back, so each was about half as "thick" (far from my body), but there isn't a lot you can carry in front of you without seriously impeding movement.

Anyway: force times distance equals work.

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.

No it does not.

Two kilograms extra is gigantic.

If you have a friend who hikes or backpacks, ask them to take you along for your first time and try it out for yourself.