First, no one is buying these laptops because they are feather light. Second, Compared to humping your desktop 4090 machine around, these laptops are feather light.
The point is mobility. I have an ASUS gaming laptop, 17 inch. It's big and bulky and I wouldn't (and don't) use it as my primary mobile computer. But, it's awesome that when I travel I can bring it along and play the games I like to play on it. I travel between 2 homes on a regular basis and I don't have to sacrifice not playing or having to spend 2x on 2 gaming desktops. I also solved the power brick problem by getting 2 of them, one for each location.