You must not be keeping your shields up on your toons. There's simply no way that they do that much damage, especially on normal. Are you smashing 1, 2, and 4 TOGETHER? Like, CONSTANTLY? Cause you should be. Also you don't have to wait until you are dismounted to switch - you can simply click on another horse when your horse is low and you'll jump onto it seamlessly. Read the post I linked above - it' not pretty, but it's simple and effective.