As an archer I don't find that rain does a massive amount either way, I wasn't even aware that it changed damage (because really, 10% isn't a massive amount if you're hitting a light armored target, and isn't a massive amount if you're hitting a tank-y target).
I was under the impression that rain also slightly alters the projectile's flying physics, by slowing down projectile speed very slightly.
Or at least, when it rains I seem to have a very slightly harder time hitting things, and also tend to hit allies more when firing at people who are fighting.
But even with that, rain isn't a huge deal.
It's just a bit silly that there's a randomized effect that nerfs some builds but doesn't do much at all to others. As has been pointed out, maps can favor certain builds, but there is a diversity of maps, so when the map changes you're as likely to end up a map that is "good" for you as you are one that is "bad"... whereas rain is pretty much 100% never good for ranged, but there aren't really any weather effects that specifically disadvantage melee (as a whole) or cav.
It'd be nice to see, say, a maneuverability decrease for cav in rain, due to the possibility of slick terrain.
Fog is a good example of nice weather, because on one hand, it makes archers less visible and able to snipe better, but on the other hand it gives the melee concealment, and also makes it riskier for archers to just shoot at vague outlines because banners can be hard to see in it. Similarly, cav can come out of nowhere to hit melee, but cav also have a harder time seeing who is carrying polearms and is ready to rear them. I would like to see more mechanics like that, and less mechanics that effect specific pieces of certain builds.
Either way, there are much worse things as an archer, like how arrows weigh more than a great maul.
-My $0.02
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