The most hilarious thing about complaints about IB is that it isn't a one-shot skill unless the person getting one-shot is low level or really undergeared.
I'm pretty well geared as mages go (well, for Palenque anyway) and on my p/s, I rarely one-hit anyone. I need 2 shots at least, usually three. I have about 104k buffed for siege, and rogues, scouts and sometimes mages smoke me with one hit. My IB on the other hand, only hits for between 35-85k depending on crits and the mdef of the target, and almost anyone I try and kill has at least 100k+.
Putting a CD on IB would kill it as a PvP class, and make it very unappealing as a healing class, as people usually play it because it's easier to level than your average priest combo. All of those people would suffer in PvE play, and nerfing PvE for balance in PvP is a baaaaaaad idea.
Gear your own class up and think strategically. A p/s isn't at all hard to kill, and while they can hit the top of the kill charts fairly easily, they can also be dealt with fairly easily, if you send your rogues in to kill them. I spend more of my time in a siege war on top of the castle buffing than I do out on the field killing. We just look scary. In reality, most of us are insanely squishy, as long as all the people involved are close to the same gear level.