Most of the wetness isn’t what falls directly on you but what gets sprayed from your tyres and passing vehicles.
The problem was solved in the 1890s.
Full mudguards, chaincase, and wear a cycling cape. Your lower legs get damp, but that can be avoided by leggings – you can see why plus fours became popular back then.
I have spent a 12 hour day riding in normal clothes with a cape. It rained half the time and that system just worked. It is also quicker on and off than any waterproofs so you can delay the putting on a bit more. It also is eminently breathable so you do not boil in a bag.
The problem is finding a decent cape. Mine is a very lightweight one – too light. I’m looking for something more substantial.