While I understand where you are coming from, the Warlock has a immobility delay as well, unless they are in midair, and the same applies to the hunter, however I can't speak for the Titan, as I haven't used it enough to get the super. You stated that the other classes supers are instant, that is just untrue. I have been shut down countless times, in mid use of my super as a warlock. I think that the immobility of the hunter keeps its super balanced. The way it stands now, all supers can be countered, unless the player is taken by surprise, as I believe it should be. TL;DR- I think all supers are balanced the way they are.