Let me restate this: For 50 energy, and at a range of 9, you can one-shot 9 different units in the game. Those you don't kill, you've damaged and crippled for the next few minutes of the game.
I've said before that one of my bigger problems with Feedback on the HT is that it directly counters Terran's HT counter, Ghosts. (not to mention HT's cost 50/150 compared to Ghost's 100/200) Battles are decided on who shoots who first. This is not good gameplay. Did I mention Feedback has a longer range than EMP?
If EMP is too much for Protoss to deal with, then get rid of that too.