For me, riding in the rain with FD has not been a problem simply because who wants to ride in the rain anyway, with any kind of MB?
I know one can get caught out in the rain, or have the weather change from dry to wet in the course of a day IE: sunny in the AM on the way in to work and rain later in the day, or caught out and try to shoot home between showers.
As mentioned, easy on the throttle and pedal....but hey it's a bike.
Honestly, and maybe I'm just lucky, the scenarios above account for maybe less than 5% of my riding incidence. Given that low percentage, and what I account as the solid advantages: low cost, low weight, low impact on the frame, ease of install, maintenance, and the ability to swap from bike to bike in 20 minutes, friction drive, for right now anyway, makes the most sense to me.