One thing I’ve noticed is that typical hard sided spinners gain more space at the top of the luggage than they lose out to two-wheelers at the bottom. In other words, a lot of two-wheeled luggage is not as square at the top of the bag compared to spinners. The same can be said for bags (such as Travelpros) that have a bunch of front pockets. A lot of potential volume is lost due to the design. It’s a trade off for convenience of accessing small items. If I need to maximize my carry on luggage then I’m taking the spinner.