I searched for a while for lightweight carry-on and found out one very interesting thing. There are several decent sub 4.5 pound bags be renowned manufacturers sold in Europe, but the same manufacturers do not offer them here in US. No idea why that is. Brands like Roncato, March, Samsonite, Kelsey, Brick's all offer sub 4.4 pounds bags.

My requirements were lightweight, maxing out the carry on size limit, double handle so I can stack up another bag on top and two wheels. I don't mind spinners, but 4 wheels weigh more than two, not to mention they stick out more, so you actually get smaller bag.

I chose American Tourister Lightway Upright 55/20 (Samsonite brand). I could not be happier about it. ~$90. Solid build and astonishing 3.3 pounds. It's a no frills decent looking carry-on. https://www.alzashop.com/sport/ameri...tm#alternativy

My other bag is Tumi and it weighs exactly double! Obviously it's lightweight, so probably not as durable, but I think it will last 3 years with little care and making sure baggage throwers never get their hands on it.

As I said you can't buy it in US, but maybe you can find it online, or buy it while in Europe.