Frollo is realistic in the worst way.
He's human. He's a realistic depiction of a tyrant. A xenophobic, perverse tyrant.
And it's terrifying, because he's just human, but he alone basically owns Paris. He alone basically treats the word of God. He alone is a monster, because he's human. Gaston and Tremaine are realistic, yes, but they're also played up for laughs and are extreme depictions.
Frollo is just what he is. A monster. The only villain I can think of that represents all 7 sins.