I think maybe you overestimate how big a problem water is.
It's a 12v system, the switches are not submerged (normally, but in my trail bike days it has been known), rainwater isn't very conductive, and they are facing to the rider not the oncoming onslaught.
In all my bikes, they have been simple slide switches, nothing more.
Here's a video of some fellow disassembling some typical switches,