Both of you have wandered off into the weeds.
An excommunicated Catholic is still a Catholic, but a very bad one who can't practice any element of his faith until he formally, explicitly (sometimes even in writing), repents to a church authority with faculties to forgive the offense in question. (Which authority depends on the offense.)
Neither the Pope nor any other human can undo a valid baptism, since it's Christ through the Holy Spirit who baptizes.
The whole question of "was Hitler excommunicated" or "why didn't the church excommunicate Hitler" is a silly one. Hitler was perhaps juridically* a Catholic, but certainly not a Catholic communicant after 1918. Denying him privileges he didn't exercise (and of which he was completely contemptuous) is a meaningless and futile gesture. And canon law automatically took care of that gesture anyway through his acts of murder against priests and religious.
Moreover, an excommunication is meant to spur someone to repentance. Do you think it would have worked in Hitler's case? I certainly don't, and I see no evidence from any aspect of his career that would lead me to believe otherwise.
*Someone who has "defected from the faith by a formal act," e.g., by professing another religion -- Hitler described himself as a "pure heathen" at one point -- is excused from various aspects of canon law which bind only Catholics. However, it's a stretch to say that even they "aren't Catholics anymore," because they can typically return to the faith simply by repentance and confession. As I say, there's no way to unbaptize someone.
It’s still excuses.
The church should have taken the action.
I know Protestant denominations who have removed people from membership rolls as an official act and statement by the church that they will not tolerate that kind of sin in their congregation, even when the people tried to beat them to the punch and asked to be removed.
They felt that the fact that the person asked to be removed in anticipation of the official action of the church was irrelevant and they did it anyway, so that people knew where they stood.
It leaves NO doubt about where the leadership of the church stands on the issue, unlike the situation we have here with the RCC where who knows what is going on with the Vatican’s position on homosexual and pedophile priests.
It sends the message that they really don’t care and that all they’re doing is looking out for their best interests.
The Catholic church should have taken a stand and made it official with Hitler. Presuming that the action would not have made any difference is showing that they know what’s in the heart and mind of the person and nobody can know that.
The Catholic response to not taking action is that of giving the sinner time to repent. However, here they decided without knowing the heart and mind of Hitler, that he was beyond repentance. What a gutsy assumption to make.
Not that I think he would have changed, but Saul was converted.
It would do the RCC a lot of good to be consistent in how it applies its policies. They would save themselves a lot of trouble, trouble they bring on themselves.