When I used to be cav and we had our match against Astralis I had zero difficulty sniping out Agile, which I felt turned the fighting heavily in our favor. I was using a courser + great lance + bastard sword + my normal armor. Before I started spawning in as cav, it felt like the matches were a lot closer, because Agile hurts a hell of a lot. There were many variables in the outcome of the match of course, but taking out a really good archer in an 8 v 8 I think is a very important key, at least if your team is composed mostly of 2-hand heroes.
It's not a matter of skill on cav (the independents can tell you how good I am on cav), the map chosen just worked laughably well in our favor. We fought on a map that was more or less split down the middle by a huge cliff, so while my team went one way to go engage their team I went around the back where the range have to hang out and because I was using a courser, they had very little time to react by the time I came charging up.
So I guess what I'm saying is cav isn't useless, you just have to use it at the proper time. We went from having nail-biter fights, to our last round being a flawless victory.
-idlewind