Idk, I have Toyo ATs on a truck now (where it rains everyday, lol) and had AT3 Coopers on another one ,F250, a few years ago in WA and AK. No issues with either. And I dont slow down for rain and typically not for snow either unless traffic dictates.
It's about tread depth and amount of voids for the most part for hydroplaning. Some tires have special channels in the tread to help with hydroplaning, but that's pretty much just car tires and ones with a lot of contact surface and not many voids (good for pavement traction, not great at getting water out from under the tire).
I have my favorite tires for sure, but yes it is pretty much that simple, IMO.
And having tires siped, while it does cut down on tire life, if loaded heavily, improves traction pretty much across the board, especially on slippery surfaces. It does not improve traction in straight line acceleration or cornering if you're nearing the limits of traction on dry pavement, because they act like snow tires and the tread moves around too much.