There is no other card in the two first sets that can do 30 range damage. On top of that, the range of 10 is very long for the power of this range damage. He also gets the ability to deploy around the board. The best comparison for War Wizard is Shadow Mastiff, who is also level 4 Dex, but does only 20 melee damage. Shadow Mastiff does have 20 extra HP, but the utility of massively powerful range damage and the raw strength of the intelligence spells such as Arcane Ritual and Shield just trump Shadow Mastiff in every respect. This is looking at the raw card itself, not including the synergy involved with cards like "Heroic Surge" or "Behind Enemy Lines" due to the wizard being an adventurer.
War Wizard is simply more powerful than any other creature released so far, and any competitive army will be running at least 3, but more likely 4.