"As wizards go" means that you're comparing this fellow to other wizards. "As.....go" is usually used in a humorous way, meaning that you're trying to find one good thing/person among a crowd or bad or strange or unusual ones.
For example: As death sentences go, the electric chair is not a bad way to die.
The soybean and alfalfa sprout sandwich wasn't too bad, as health foods go.
Our room at the Motel 6 was surprisingly clean and comfortable as discount lodging goes.