Brake effect at Legacy on very wet road

My Subaru Legacy, spec b, 3.0L (Jg 05) shows almost no braking effect on very wet roads, especially highways and strong “water spray” of the driving vehicle. During braking, a audible roaring like a bicycle on which the brake blocks do not reach the rims cleanly and there are strong vibrations. Even if the brake and re-activation are released for a short time, the faults remain. It cannot lie at the balancing of the brake pads, this has the G aragist already changed three times and usually also have to grind immediately again clean, because of forgone and the resulting vibrations also on dry road (was already a topic here at the outback ). With dry roads or only slightly wet roads there are no brake problems. Rims and tyres are original parts. Does someone have similar problems with the brakes? Or what can it be, because Subaru Switzerland apparently knows no such problems with the 3L Legacy. Thanks e for feedback