So, "suction" is what brakes you. Just perfect.
You realise that it is not the suction on your stones that sharpens the blade, right?
Lack of friction is also the reason your rim brakes are much worse in the rain.
Since you are absolutely sure it is not friction, perhaps you really do need to try, say, spray-on silicon super lube on your rims. Or even WD-40, as I bet you get more "suction" if you have oil there as it makes for a tighter "seal".

As for not worrying, you polish your rims when you have been out in the rain. I bet you'd polish your disc rotors too.

Since we are apparently sharing "stories", I thought I'd share one that is at least a bit relevant:
I have Shimano Saint downhill brakes on mine - with sintered pads. I have a Rohloff 180mm rotor at the back, but a Shimano Ice-tech 203 mm rotor at the front. As my bike is a cargo bike, there is no way I'm doing an endo so I don't have to worry about that. If I get something on the rotors, I can't brake as hard, but roughing up and cleaning the rotors (and pads) with alcohol makes it possible to break hard again. I'm glad you're not riding your bike behind me and not paying attention, because you wouldn't be able to stop before hitting me.