A burst heal on a 90s CD, even if only for 25% of your health bar, is absolutely is worth a tank defensive cooldown. As you well know, damage taken only matters if it kills you (which tends to be burst). Something like GotN’s HoT, or in your example, Frenzied Regen, are weak relative to direct heals because the benefit is spread out over time and counteracts burst damage poorly.
As I implied before, one tick of Regeneratin’ would be almost be on par with reactionary emergency heal CDs like Vamp Blood and Last Stand. If one is skilled enough to fit in two ticks, it’s not even a question.
But if you don’t want to compare it to a tank defensive cooldown, compare it to the Warlock Healthstone (which is a friggin’ class-defining utility). Use Regeneratin’ for 2s, and it’s healed for more, and even if you only manage 1 tick, it’s available more than once per combat period!
EDIT(s): Rewording arguments and I don’t know how to use these new forums.