One thought.
Did a ton of shopping the other day with these uber large panniers.
https://www.ortlieb.com/uk_en/back-roller-pro-plus+F5252
Since it was shopping there was more weight in there than there will ever be camping or touring.
They were mounted on a quality Tubus rack but even so I couldn't help wondering whether the whole mega load was more stable/less wobbly than it may have been with a 700 bike since it was a tad closer to the ground. Solid as a rock.
Maybe I'm deluded.
Does my idea make any sense?
You will certainly get less flex on a 26” wheeled bike which will have more compact triangles forming the frame. Plus less flex in wheels. On lightweight 700c wheeled bikes you can certainly get tail wagging the dog if you’ve got heavy panniers fitted and are out the saddle going uphill.