You are comparing apples to oranges, and also forgetting an important dogmatic truth.
The decrees you cite are disciplinary in nature. The Conciliar decree from Florence is dogmatic. Even if there were certain flawed presuppositions on the part of the pope or council defining, what is defined itself is infallibly true and dogmatically binding. (I’m not saying there were flawed presuppositions here, but am merely noting this for the sake of argument.)

Also, the dogmatic truth that renders your argument moot is that it does not matter at all how culpable one is for not having faith. Faith is a prerequisite for salvation, and to say that we are all somehow owed salvation without faith is pelagian.

http://www.nativeweb.org/pages/legal/indig-romanus-pontifex.html
\The Roman pontiff, successor of the key-bearer of the heavenly kingdom and vicar of Jesus Christ, contemplating with a father’s mind all the several climes of the world and the characteristics of all the nations dwelling in them and seeking and desiring the salvation of all,
wholesomely ordains and disposes upon careful deliberation those things which he sees will be agreeable to the Divine Majesty and by which he may bring the sheep entrusted to him by God into the single divine fold, and may acquire for them the reward of eternal felicity, and obtain pardon for
their souls. This we believe will more certainly come to pass, through the aid of the Lord, if we bestow suitable favors and special graces on those Catholic kings and princes, who, like athletes and intrepid champions of
the Christian faith, as we know by the evidence of facts, not only restrain the savage excesses of the Saracens and of other infidels, enemies of the Christian name, but also for the defense and increase of the faith vanquish them and their kingdoms and habitations, though situated in the remotest parts unknown to us, and subject them to their
own temporal dominion, sparing no labor and expense, in order that those kings and princes, relieved of all obstacles, may be the more animated to the prosecution of so salutary and laudable a work… We (therefore)
weighing all and singular the premises with due meditation, and noting that since we had formerly by other letters of ours granted among other things free and ample faculty to the aforesaid King Alfonso — to invade, search out, capture, vanquish, and subdue all Saracens and pagans
WHATSOEVER, and other enemies of Christ wheresoever placed, and the kingdoms, dukedoms, principalities, dominions, possessions, and all movable and immovable goods whatsoever held and possessed by them and to
reduce their persons to perpetual slavery,…\

To reconcile these two decrees we have to assume that Nicholas V assumed that all non-Christians were \enemies of Christ\ and that latter Popes corrected this. The same applies to Pope Eugene. He assumed that all non-Catholics were culpable for their state

The quote above in bold is from a book written by Saint Fulgentius (who died in 533 AD) called “To Peter on the Faith.” The original (translated) text from that book reads as follows,

“Most firmly hold and never doubt that not only all pagans, but also all Jews, all heretics, and all schismatics who finish this life outside of the Catholic Church, will go into the eternal fire which was prepared for the devil and his angels.”

The Council of Florence elevated Saint Fulgentius’ teaching to that of the Solemn Magisterium of the Catholic Church, which made it forever infallible, and per the following solemn definition given at the First Vatican Council,

Pope Pius IX, Vatican Council, Session 3, Chapter 4, ex cathedra: “Hence, too, that meaning of the sacred dogmas is ever to be maintained which has once been declared by Holy Mother Church, and there must never be any abandonment of this sense under the pretext or in the name of a more profound understanding.”

we are forever restricted to understanding the solemn definition given at the Council of Florence as it was defined at that time. Saint Fulgentius’ words are, I think, pretty self-explanatory, as is the text from the Council of Florence.