DPS is the factor in all of this. Let me stress: Damage Per Second. Opening with Blizz III is flat out lower DPS. The timer, meaning the "seconds" in DPS, is started the exact moment the boss is engaged. You're getting a 240 Potent Blizz III, 270 Potent Thunder, and 168 Potent Fire III (with potential procs). Thats 678 potency in the first 8 seconds. In the same 8 seconds, you could have dealt 1238.4 potency. Anyway you swing it, there really isn't a comparison. You also have to factor in, Fey Wind is cast immediately, as well as Balance. Battle Litany on drgs 2nd GCD, and Trick Attack shortly after. You're wasting valuable time on small potencies and your potion isn't even up yet.

The point is to kill the boss as quickly as possible. Thats your job. You might be able to add an extra Fire IV or whatnot, but your actual DPS will be lower because its taking you way more time to "ramp up." Plus your missing out on party buffs as well.