My business as a travel consultant and experience over many years is that the airlines do not go by their own rules and it depends on the gate agents, the load of the plane as they can take and gate check a perfectly sized bag if they are running full at anytime, equipment can change and regional jets the overhead bins are too small for anything 22 inches. I carry a cloth shopping bag and remove my laptop and camera and carry it onboard with me and jetway check my rollerboard bag living in a city with lots of regional jets. I have had the airlines take my legal size carry on at the gate so many times at LAX I went and purchased a smaller one as for work I always have my camera and laptop in that rollerboard versus carrying the weight on my shoulder. I often wear a safari type jacket with lots of pockets even a zippered pocket in the back that my netbook fits in. This comes in handy overseas with carry on weight limits of 7 kilos and only 1 item as I fill the pockets with extras I would usually have in the carry on.
Use the Sony RX10 III for those travels which I am very happy with its quality and size and weight while traveling.

I am a travel consultant and travel all the time. With airline restrictions especially intra country smaller airlines baggage, including carry on is severely limited. I find my SONY RX10III amazing to capture all the different types of shots presented. Before purchasing I read tons of reviews and professional photographers were giving it a thumbs up. I have now been to Vietnam, Cambodia and India within the last year or so and have been very satisfied with my pictures. When touring and moving all the time and being with others even with private touring you don't have that much time to stop and set up anyway unless you are with a photography tour. I think the newest model is now the IV. If you plan on lots of travel in the world worth looking into.