Just because the Catholic church calls someone a saint, doesn't necessarily make them one. On the other hand, just because you call someone a grotesque tyrant, doesn't necessarily make him one either.
God decides whether he was a saint or not. Water, Baptism doesn't save you. And deathbed baptisms were apparently common in the 4th century.
One minor correction: at that time there was no Catholic or Orthodox or Protestant - just Christians and heretics.
And, likewise, just because the catholic church says a just morality can only arise from the bible, doesn't necessarily make that true, either.