I lived off the back of my motorcycles for 6 years. In the rain I always wore rain mitts. They fit over your regular gloves, and are completely waterproof. I imagine they would be cumbersome on a bicycle but if complete dryness is what you're after then that would be an option. Personally, I just ride with regular gloves, fingerless or otherwise, on the bicycle. I am not bothered by wet hands on the bike (I guess the motorcycle is different, in 100+ mph winds, lol). The other option, what we use for emergencies on the motorcycle, is to wear surgical gloves UNDER your other gloves. Won't keep your gloves dry and will be clammier than the first option, but they will at least give you full finger movement. There is also an emergency solution for keeping your feet dry on the motorcycle, and that is a bread bag over your sock. But there are also rubber booties that fit over your boots (or in the case of a bicycle, shoes), which are made for motorcyclists. If you want 100% effective rain gear then the motorcycle shops will have it. Motorcycle rain gear is also made to withstand extreme winds, and will not tear under any condition. It's hard to find raingear which is also durable. A 2-piece rainsuit for motorcycles will last you forever, besides keeping you 100% dry. But it'll also cost you in the hundreds and will not be the lightest thing, and could be cumbersome and not allow precise movement. I'm just giving this option because you seem particularly concerned about full waterproofing. Personally, I have learned simply enjoy partial weather resistance on the bicycle. (though on the motorcycle I take rain gear VERY seriously)

Basically, finding 100% effective rain gear is very easy. The problem is that there are compromises you always have to weigh. Your 100% effective rain gear may not be 1) lightweight or 2) fitted for easy or precise movement or 3) very affordable.