JJoseph, you need to stop self-interpreting Scripture and listen to the Church's interpretation of these matters. See below the DOCTRINAL TEACHING from Pope Eugene, which contradicts your comments above, and which you MUST accept, under pain of sin and hell.
I cited the Church teaching of Pope Leo XIII and the Baltimore Catechism, which you rejected and didn't even address. Also, the words are plain, and every Catholic commentary confirms them, as does the Magisterium of multiple Popes including Pope Leo XIII, Pope St. Pius X and Pope Ven. Pius XII.
You are totally ignorant of what the Council of Florence even was about and what it is saying. It is not addressing catechumens at all, nor those seeking Baptism for the first time, nor ready to die for Christ. Rather, it was a re-union Council between Greeks and Latins, and it's a clear admonition to persevere in the Unity of the Catholic Church after having once attained it. Ironically, this is precisely what you Dimondists et al have not done, whereas the Eastern Catholics did it, while the Greek schismatics did not. You are Latin schismatics and not Latin Catholics if you defend separation from Rome, whereas some Eastern Catholics, especially Russian and Ukrainian Catholics preferred horrible death and torture under Communism to remain in Catholic Unity with the Holy Roman Church, which the Council of Trent calls the Mother Church of all Christendom, and Fenton teaches is indefectible even as a particular local Church.
The Council is thus speaking of those who commit the deliberate mortal sins of heresy and schism and then think that, provided they are martyred for Christ, then their unrepentant mortal sins will be absolved. It won't. Neither will yours, unless you specifically repent of yours. So Cantate Domino is not addressed to Eastern Catholics. It's addressed to schismatics, whether Eastern or Western, whether ancient or modern. Reflect carefully on it and try to practice it yourself. It in no way condemns Baptism of Blood, or the great glory of martyrdom for the Lord Jesus Christ.