Well the only thing I concern myself with now is the win %. I am contributing to my team and helping us win or not? Most of the time I find myself going medic because my team either has just one or none. But I WILL change class as needed given whatever situation. I'll fully admit I'm stubborn sometimes and am dead set on playing one class because that's what I want to play.
This is TEAMfortress 2 so I don't really think the stats tell the true story. Phantom is on top but has a win ratio of 29% which is nothing spectacular. (mind you my win % is worse). Take this random person I found in stats. pilvlp Win 62%. Why is this person ranked 2491 (as of this moment I type this) when this person is, no offense to phantom, clearly a more valued person to have on your team. Perfect set up and having this person on your team means you'll likely win more than half the time.
Stats show how many points a person has not their team value. That's my 2 cents for now.