understand.
PI does not refer to a pope being granted the power of never being wrong. It does not empower the pope ate all, but actually does the opposite. It protects the Church from a corrupt pope. A pope may be corrupt and try to change Church teaching, but PI prevents him from ever changing the doctrine of the faith. Even the Medici era did not result in doctrinal change.
In the present day, we see what I believe to be a pope who wants to, but cannot change the doctrine of the Church.
Marriage is still a sacrament between one man and one woman. Abortion is still a grave moral sin and the killing of innocent life. You see Francis trying to work around the edges constantly, and leaving questions he should quickly handle unanswered and unaddressed, but never does he change the doctrine of the faith.
PI is a fail safe that limits the power of a misguided or simply bad pope. The popes do not differ in their handling of doctrine of the Church.