But in reality, it’s the same old chestnut, say 90kg body weight plus 18 kg bike weight, = 108 kg. If you manage to take 2kg off the bike, that’s still 106 kg total.
If you weigh 70 kg plus 18 kg = 88 kg less 2 kg is 86 kg total. There is nothing to suggest a person weighing 70 kg is any less strong at riding than someone of 90 kg, so guess who has the advantage.
Now then , if you were to change your GT @ 18kg for say……a Schlitter Encore @ say 10kg, then yes big difference, but it wouldn’t like to go off road, or go touring, and unless you actually put the miles in, would be slower than your upright.