Thanks
@aerobod and your links were interesting in suggesting that because my last two cars have had Pirelli Winter Sottozero (Serie-II and S3 respectively), that's probably why I have the view that winters are much more resistant to hydroplaning than the summers, because they are, especially in the case of my current S3s.
It also underlines the danger of generalising across different seasons to say that all winters are inferior to all summers re hydroplaning. Just take a look at my Winter Sottozero S3s (right) compared to my summers (left):
On the basis of my own experience, the S3s are simply better than my summers in heavy rain and standing water in the colder winter months. And when you look at the area of the tyre with drainage channels and the much more extensive routes for water to escape, this should come as no surprise. No doubt someone will rightly point out that my stock Continental summers aren't the best brand to chose from, but that also sort of proves the point about how difficult it is to make generalisations, even within the same-season brands, let alone between seasons.
A while ago I had a long discussion with someone who asserted that summers, having mainly straight drainage channels (as on the left), were the most efficient at moving water from under a moving tyre. So I did a bit of research into some of relevant tyre industry published research, which indicated it wasn't that simple, or true. Around a 20° angle of the drainage channels shifted the maximum water (which may explain why some of the all-seasons are good, because trads like the CrossClimate are very diagonal). But as someone referenced, having the whole tread with angled channels was not good for braking, so it's something of a trade-off.