My only experience of hydraulic discs is on a Bullitt cargo bike, which was in the mostly dry except for one downpour during which I was sawing up a tree with Kappers and Dave.
I will now pause this post to thank chdot for creating, albiet unintentionally, the circumstances by which I could or would ever have written the previous sentence.
Where was I? Oh yes. Those brakes were beasts, but there's enough variables between the handling of a Bullitt loaded to its full 204kg tare and my Croix going at 45mph that I need further study to be convinced of the gulf between cable and hydraulic. I expect this study would be very short. Basically a quick blast and crash-stop on a 700Cx2*mm slick-tyred hydraulic device.
This morning I set out on the stiff little fixer. No brake at the back aside from my legs; Ultegra(with default pads) caliper at the front. Forecast was dry. Meh.
This lunchtime's rain was the first time it's had to slow me down in proper wet and while it's still the best rim brake I've had, I was unpleasantly surprised by the lack of its usual grab.
That isn't to say I felt unsafe - if I've been on my other two rim-brakers for a while I normally have to remind myself before touching the lever on the stiff little fixer to feather them for fear of a yanked yarble, so there was still plenty of horsepower there.
Once I was home for lunch, I swapped to the cable-disco-baby Croix and for the zillionth time marvelled at how nearly complete its indifference to weather is.
TL:DR - rim brakes are bobbins in the wet. Discs of any kind are better for that reason alone.