While this might be true in a certain way, the reality is that we can imitate the saints.
The key lies in finding the essence of their life and what enabled them to live a heroic life of sanctity.
Secret of St. John Vianney's life
St. John Vianney is one of those priests who at first glance seems too "crazy" to imitate. He remained in the confessional for hours every day, ate only potatoes, and would daily fight with the devil. His bed even caught fire during one such battle!
Pope Benedict XVI brought-up this same problem in a general audience in 2009:
The pastoral methods of St John Mary Vianney might hardly appear suited to the social and cultural conditions of the present day. Indeed, how could a priest today imitate him in a world so radically changed? Although it is true that times change and many charisms are characteristic of the person, hence unrepeatable, there is nevertheless a lifestyle and a basic desire that we are all called to cultivate.
He then drilled down to what he believed to be the secret of St. John Vianney's life:
At a close look, what made the Curé of Ars holy was his humble faithfulness to the mission to which God had called him; it was his constant abandonment, full of trust, to the hands of divine Providence. It was not by virtue of his own human gifts that he succeeded in moving peoples' hearts nor even by relying on a praiseworthy commitment of his will; he won over even the most refractory souls by communicating to them what he himself lived deeply, namely, his friendship with Christ. He was "in love" with Christ.
It seems so simple, yet in practice it is very difficult!
All priests (and in reality, all humans) are called to an intimate friendship with Christ. It should be our goal to be "in love" with Jesus Christ.
St. John Vianney did not rely on his own skills, as he admitted how weak he was and full of imperfections. He knew that he could do nothing with out the help of God.
A modern-day priest might not be able to spend hours and hours in the confessional, and he should probably eat more than potatoes!, but he certainly can imitate St. John Vianney's personal love of Jesus Christ.
If a priest can do simply that, he will be on his way to becoming a light for his parishioners.