Everyone's experience is different, I suppose. Your Rimowa does not go down the aisle any "easier", it's just narrower. They either go down the aisle or they don't, the Costco case goes down the aisle just fine. Yours has more room on either side, to be sure, but that's simply because it's an inch and half narrower.
Rimowa Salsa Air Cabin: Dimensions: 21.7 x 15.7 x 7.9
Costco Beverly Hills Dash: Dimentions: 22.5 x 15.7 x 9.5
If you fly internationally that's important. I fly only domestically, and it's not important, I like the extra space in the Beverly Hills. There is no benefit to having an international sized case--if you don't fly internationally. My point here is if it works better for you because you fly internationally great. But don't state that aw a big advantage of the Rimowa over the Costco. For me it's detrimental.
Rimowa Salsa packing system
Frankly, I don't see a big difference here. ???? You like the second zippered side as opposed to the elastic tie-down strap. OK.
About your Costco not fitting in an older jet with drop-down bins, I think that's a rare situation. The Costco fits in every Southwest jet I've ever flown, just dandy. Much better than my B&R Baseline.
The wheels? Just because of this I'm going to go to a luggage store to look at them, but I'm willing to bet the Rimowa has the same or very close to the same Hinimoto wheels.
Are there differences? I'm sure there are. But one is $50 and one is $475! In my review I was careful to say most reviews here are based on preferences, and that's true. How we like to travel, how we prefer to pack, what sizes and features we need or want. I don't take issue with you preferring the Rimowa, it's just that you are kind of knocking the Ricardo.
I don't know which one is 'better' (if that can even be determined), but I do know there is nothing which justifies the Rimowa being 9.5 times the price. There just is not. And I'm not against top tier luggage
when there are differences which justify it. Like my Tumi Alpha laptop brief. I don't like it because of the name plate, I like it because it's bomb-proof. There is much more in the value proposition there relative to other briefs.
I still contend there is very little difference between most of these hard-side spinners, and no reasonable person would conclude there is a 9.5X price swing in value between these two.
You like a smaller bag, that's fine. I would not suggest domestic US travelers will have a lot of trouble with this bag in the overheads because it is simply not true. If you fly 3-across commuters all the time you have to consider that. Buying a European sized carry-on for someone who does not travel internationally because once in a blue moon you might be on a plane with weird overheads makes no sense, IMO.