That build relies on a 4 second buff, so the counter would be to either CC the Warrior, or kite them during that 4 seconds.
Most classes have some sort of teleport, the ability to purge CC (because the warrior will open with a knockdown/stun), or to turn completely invulnerable for a short time.
Also, the Necro has some abilities that make your buffs turn into debuffs.
I bet there are actually many more counters to it that I am not even thinking of. And considering that ranged can do damage while kiting, and there is no interrupt code, I hope it stays.