Hand fatigue is a real issue if doing big off road touring, but that’s not most people.
Yes rim brakes are worse in the rain, but they’re not that bad! I wonder if people who say this have tried a modern dual pivot road caliper or decent v-brakes. They have easily enough stopping power for commuting in rain.
Everything sucks in the rain. They still work alright they just take a single rotation to squeegie water off the rim then they grab stronger than the tire can hold the road.
I've never heard of the hand fatigue thing. I agree that it sounds like BS.