I have the opposite experience. If I play normals it's always a horrible pubstomp one way or the other. I see almost no warding, people actively quitting, AFKing, or trolling, refusal to play support, and massive raging and negativity. In ranked, I get generally even matches and things work out (most of the time; occasionally the bad stuff shows up in ranked too).
Part of it is how often I play, I think. I play ranked almost elusively and only fall back to normals to try new characters and builds. This probably results in my MMR being horribly out of date in normals, since I have improved a lot since I started playing ranked. So I think it has more to do with how often you play each mode.