While it is true individuals spoke of those as heretics, that was not official teaching. When I was a kid, there was still a few hard cores teaching “Limbo” as Doctrine. It never was a doctrine, it was a theological speculative opinion to a theological question regarding the fate of unbaptized infants.
There were lots of things presented as doctrine that were not. Of course today we many times have the other extreme, things that are Doctrine are watered down or not taught as such.
Now again, there are things in the protestant faith that are heretical [that would contradict both what the Catholic Church teaches as well as the Orthodox]. So I have no qualms of saying there are heretical beliefs in Protestantism. To call a protestant a heretic for denying the Catholic Faith when they have never embraced it is where I stop. On the other hand, there are many FR Prots here that are outright Nestorians and I will point blank say they are positing heresy then they attack the Doctrine of Mary, the Blessed Mother, as “Theotokos”, but many of them are taught by the local Pastor Jim, or Reverend Bob who cites the Bible [of course] and interprets it according to how “he interprets” it apart continuity with Apostolic Tradition.
So, I guess Pope Leo XIII was wrong here.