Sir,
Yes. Wild Changing is the tactic that grants 15% crit.
To the questions on why it should modify the cooldown of Firestorm? This was the state prior to the moving of Firestorm to the Changing Mastery line. My understanding was the swap of Firestorm and Indigo Fire of Change was for more thematic unity (making single target and AOE abilities consistent in the mastery that focuses on each). It was not to weaken either ability. As things stand, Firestorm is weakened. Why? Firestorm is now unable to perform like Sorc Pit of Shades or BW's Rain of Fire. Sorcs have a cooldown modifier for Pit of Shades from the tactic Neverending Agony. . BWs have the same for Rain of Fire with the tactic Fiery Reserves. This makes magi less desirable or effective to either counter BWs Rain of Fire or match up as an alternative to sorc Pit of Shades. All through Live, Firestorm was a joke. This changed. I would not like to see a reversal in the progress.
If it is a choice between thematic consistency and having an effective ability, I would opt the latter. If Firestorm is to be in the Changing Mastery, please apply the cooldown to Wild Changing so the ability remains viable, as it was before the swap.