What advantage did Chillingworth have over Dimmesdale?

Basically Dimmesdale was sick in body and soul. Chillingworth claimed himself a doctor. This along with a manipulative personality gave him a hold over the sickly priest.

He had a clear path, in which he could conceive a more personal revenge that no one else could.

His advantage was found in cold, calculating maliciousness. Aslan nailed it on the head with the word "manipulative." It the old, 'keep your friends close but your enemies closer' concept. He didn'y just want to have a hold on Dimmesdale; he wanted to destroy him inside and out.

"Calm, gentle, passionless, as he appeared, there was yet, we fear, a quiet depth of malice, hitherto latent, but active now, in this unfortunate old man, which led him to imagine a more intimate revenge than any mortal had ever wreaked upon an enemy. To make himself the one trusted friend, to whom should be confided all the fear, the remorse, the agony, the ineffectual repentance, the backward rush of sinful thoughts, expelled in vain! All that guilty sorrow, hidden from the world, whose great heart would have pitied and forgiven, to be revealed to him, the Pitiless--to him, the Unforgiving! All that dark treasure to be lavished on the very man, to whom nothing else could so adequately pay the debt of vengeance!"

The advantage Chillingsworth had was that he knew Dimmesdale dale was hiding a secret sin