Any lag affects the game time. Hence, a short downpour will seem longer than it actually is in-game. That may play a part in what you are experiencing.
From memory, there is no choice on the rain:clear ratio. There is a way to keep it clear weather for x seconds, but for that to be active all the time, we would have to set up a system that automatically repeated the command every now and then.
Personally, a bit of rain doesn't hurt anyone. Players have the option of using the BetterSound (see TOG Minecraft Server Code of Conduct
) client mod to lessen the sound of the rain.