This argument is a really stupid understanding of the Council of Florence.
People who die for the one true Faith ARE united to the Church.
The Council there is excluding from salvation HERETICS who die for Christ. Such people can only have a human faith and love for Christ, and cannot be rewarded with salvation therefore. They can legitimately love Our Lord in a natural way, but on account of their heresy they are cut off from the Church, and are incapable of supernatural charity. This explains why we can see heretics are able to be kind to their neighbour. It is a natural charity, not a supernatural one.
One who has the true Faith and gives up their lives for it (which is the most dear thing a human being has) possesses a supernatural Faith and therefore a supernatural charity, which can only be rewarded with eternal life.
No, it was pretty explicit when it said "no one," and it never distinguished between a natural or supernatural faith of the person shedding their blood.
"It firmly believes, professes, and proclaims that those not living within the Catholic Church, not only pagans, but also Jews and heretics and schismatics cannot become participants in eternal life, but will depart into everlasting fire which was prepared for the devil and his angels, unless before the end of life the same have been added to the flock… and that no one, whatever almsgiving he has practiced, even if he has shed blood for the name of Christ, can be saved, unless he has remained in the bosom and unity of the Catholic Church."
I'll also add that you can't have supernatural faith when you're unbaptized, you can't have anything supernatural, no virtue, etc... unless you are baptized. Those gifts are given to you at baptism, heretics can't have supernatural faith
It's the first question the priest asks the person to be baptized. "What do you ask of the Church" and is responded with "faith"