Double Uppercut: not so interesting?

It helps a ton on single targets obviously.

DU -> FF -> FF -> DU -> rinse and repeat is amazing.

But what makes DU -> FF x2 -> repeat (I'll call this A) that much better than FF x4 -> repeat (I'll call this B)?

A is 1.98 seconds long and totals 1120% damage
B is 2.04 seconds long and totals 1080% damage

What's so amazing about such minute differences?