People in this game don't know constructive criticism. No matter how polite you are, if you just tell the DPS, "do you think you can step it up at this phase?" is going to be met with hostility. Why? Because it provides absolutely no new information. And if that's all the DPS is hearing from people in the name of "constructive criticism" then it's going to wear on them. They don't need to be told that they need to step it up. They want to know what specific changes need to be made!