That list is extremely old and a few of the rankings have changed. It's a nice guide, but it's not infallible.
That said, I'll give you a rundown on the characters.
Wizard Minion is a Skeleton clone. Skeleton is the definition of average: he has all the standard magic attacks and they all behave without flaws, but there's nothing really special about him.
Necromancer is a great PvP character and an average PvE character. His Splash RTY has a lot of range and his Air RTY / RTB behaves similarly to bombs, which makes spellweaving Air RTYs particularly effective with the Necromancer. He won't trump the standard overpowered characters, but he's not a bad choice.
King is a bit of a special case. He's the only character with healing magic, but his heals are extremely weak; even at max level, you won't be healing for more than 15 or so per cast. In other words, at max level with max health, it will take about 110 seconds to heal from near-death to full. He has his uses, mainly as a tank/runner in a 4-man Free For All arena match or as an Insane Mode party healer when you just can't get past that one level, but otherwise he's somewhat lacking.
I'd prefer not to assign arbitrary ranks to these characters. They're really meaningless and I regret doing so in the past.