I have 3 bags that each weigh about 4.5 pounds empty. Already I have 2.88 [1.3 kg] pounds to play with that your heavier empty bag takes away from you. My self-imposed weight limit is 20 pounds [9 kg] fully packed.
None of my bags is hard-sided. All are 2-wheeled. All have T-shaped monopoles. All are very simple in design with limited external pockets. Those features, or lack of them, help to make them lighter. All are old and no longer available except maybe used.
There are newer versions that may be heavier or have less capacity. I always look at other suggestions, but so far have found nothing better than what I already have. Note that I jumped to the bait when they were on sale, so I didn't pay full price for any of them.
These are my current bags:
Osprey Ozone -- neither is expandable.
- T-shaped handle. 42 L. 55x36x23 cm. [21.6x14.2x9 in.]. This is the typical US airline size and has the largest capacity, but its shape makes it harder to pack.
- Global. T-shaped handle. 38 L. 50x40x20 cm. [19.6x15.7x7.9 in.]. Note the difference in shape -- shorter, wider, shallower. This is my favorite. In spite of the limited capacity, it's the easiest to pack.
Eagle Creek International Load Warrior -- Expandable, but I've never needed to do that.
T-shaped handle. 36 L. 53x35x20 cm. [20.8x13.8x7.8 in]. Expands to 39 L. 53x35x24.5 cm. [20.8x13.8x9.6 in]. Note that it expands in depth only.
I use Eagle Creek compression packing cubes as my primary packing organization tools and a few other packing cubes that are not compression ones. They help make more room in my bags, but taking the air out doesn't lighten the load.