This thread misses the point of Blizzard 4. You have to typically wait for 2 ticks of mp gain to get full mp, which you obviously want.
Blizzard 4 was created in order to satisfy that. In fact, many times you need a little under 3 GCDs if you're unlucky with server ticks, which is also one of the factors of why people use thunder during ice phase.
You don't use blizzard 4 for it's sweet damage or anything like that. In fact, I'd bet if blizzard three just gave you a full mp bar upon casting, you wouldn't even want the umbral hearts.

Blizzard 4 is there because BLM needs another skill to use during ice phase to fulfill server ticks. The dev team saw this, and gave them a low damage utility spell in that slot.
If you already have a full MP bar, like say, in your opener, it's not necessary to fluff up your blizzard phase with another cast.
Blizzard 4's "issue" as described by people here is literally that it fulfills it's role of a utility spell to cast while waiting for your MP to come back extremely well.

It's wonderful at the moment. It needs absolutely no change whatsoever.