First of all not one pope of the U-turn in history actually challenged or rejected as papal the 1616 decree. Neither did God allow any pope to give Galileo an official retrial. As Catholics we have God's promise that popes do not make mistakes when using their office to define a heresy or a dogma.
Yes, true. If a pope had done that, he wouldn't have been pope in the first place, or would have ceased to be pope when he did. That is obvious, given God's promise.
Additionally, it is against basic reason to imagine that someone could be a Catholic, confessing the faith, and be a heretic at the same time. This applies to any Catholic, including any pope. So if a pope would have believed that the propositions, which Galilei was asked to confess, were wrong, he would not have been a Catholic.
On a personal note, I have no doubt every pope involved in moving the elimination of heliocentric books did so in their belief that heliocentrism was proven by science. Thus their heresy was MATERIAL, carrying no guilt or sin against faith.
First a note on terminology: The expressions "material heresy" and "formal heresy" are (to say the least) somewhat awkward. There is no matter without form and no form without matter. The whole philosophical concept of form and matter seems to be misunderstood. I know there is literature using these terms, but one should question the authors' way of thinking.
A distinction between "material heresy" and "formal heresy" is absurd. A proposition contradicting a dogma or affirming what has been anathematized is always a heresy (and never "only a material heresy" whatever that may be).
A person affirming a heretical proposition may be a heretic or in error. That is a useful and relevant distinction. He is a heretic in case he is aware of the dogma he contradicts, or "just erring", in case he is not aware of the existence of the dogma.
Now back to the said popes. Obviously you assume, that the said popes knew well, what dogmas Galilei had to confess. Practically, that's the only reasonable assumption. If you were right, and they had rejected these truths, they would have been heretics and not Catholics. In case they were heretics "only in their hearts", we wouldn't mind, how could we mind what we ignore?! We ignore what is only in peoples hearts. But if you're right and they had said or shown what is in their hearts, we would know they were heretics and not Catholics. (I recommend to never think "heretic" but always "heretic and not Catholic", maybe one should even say and write it exclusively that way.)
I don't agree with your assessment. I think you imagine these popes like many modern folk with a lack of philosophical education, who are fallen for a scientism, who make science their idol, who think fallible science was infallible. Who don't know about falsifiablity,
who are thrilled by steam-engines, cars, planes, rockets, space stations and other "magic" or magic.
Aeterni Patris of Leo XIII is about philosophy and not about natural science. It is a call to return to Thomas Aquinas and to reject the new philosophies of the obscuring "enlightenment". Not about Galilei, Newton, or the hilarious Foucault pendulum. About Kant, Hegel, Marx etc.
Aeterni Patris was published two years before the 1881 first Michelson-Morley Experiment in Potsdam, adjacent to Berlin. You can imagine, that belief in the hypnotizing pendulum must have been at the upper limit. Leo mentions the already then much beloved natural science and puts it below philosophy. Both are useful but both suffer from the same problems fallen man suffers. Both must submit to dogma. Should he think of the hypnotizing pendulum, he seems to be quite sure that the conclusions are based on bad philosophy. Today we know, he was right. I don't see any reason to assume that his predecessors where blinded by the pendulum.
Do you have any hints or even quotes for your assessment? Or what is your reason to suspect disbelief?