I really don't think one class has a distinct advantage over another. You can counter pretty much any of the things people claim are OP with a bit of fast thinking and a good aim. Self-Rez, for example, is ridiculously easy to counter. Wait 3 Seconds after they revive, then pop them. Easy free kill. Blink shotgunners are a little more difficult, but just run underneath them and turn around. More often than not, you will have sufficient time to annihilate them.