https://www.materdeiseminary.org/do-i-have-a-vocation/
I'm not a fan of using St. John Vianney as an example of "you don't have to be all that smart". About 10% of today's Trad priests could have passed the rigorous seminary training he had to undergo. Above-average intellectual capacity is definitely a must.
And the need for strong intellect is all the more important these days than perhaps in pre-Vatican II times. This requirement is out of charity ... for the priests and the souls who will be guided by him. If he doesn't have a very strong grasp of moral and dogmatic theology, he would be responsible for any harm he does.
I object very much to this idea of that you just have to be "pious" or "devout" in order to be a good priest, especially when sometimes piety masks the fact that the spirituality at the level of the intellect and the will don't run very deep. Pull the plug on the emotional inclinations and what's left is what contributes to the makeup of a priest.