"Dogmatic purity?"
Presbyterians don't believe they are the "only" true church on earth.
The RCC believes it is the only "true" church on earth.
Presbyterians don't believe their church (or any church) is without error.
The RCC believes its magisterium is without error.
Presbyterians don't believe their pastors are "infallible."
The RCC believes its papacy is "infallible" in matters of religion.
Presbyterians know there is only one Savior, Jesus Christ, our only mediator.
The RCC believes its priestcraft all to be "another Christ."
Repent.