After ten years of moving earth and building soil, we are fairly good against rain. But it does move top soil around because I till for weeds down the center of the rows. No solution but to put it back manually each year. On the upside, I have to dredge the ponds every few years. The top soil finds its way there. Fortunately, the fish and duck poop winds up there too so we get the gift of great sort of recycled top soil.
I do think heavy rain will wash away chemical nutrients. But organic seems more like a pause in nutrients. Unless your top soil is completely gone, leaving clay, I imagine the micro organisms would get right back to work making new nutrients as soon as it dries up a bit.
BTW: We got 4 inches in a day last week. I survived with only a few ruts cut into the run off area.