“”The Church of Constantine, now known as the Catholic Church, was, and is, a mixture of Paganism and Christianity.””
What nonsense!
The Church before Constantine held the same beliefs on Sacraments ,veneration of Saints,Mary,Mother Of God etc..
Just a few examples of early Church Fathers BEFORE Constantine
On Eucharist
“For not as common bread and common drink do we receive these; but in like manner as Jesus Christ our Saviour, having been made flesh and blood for our salvation, so likewise have we been taught that the food which is blessed by the prayer of His word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh.” Justin Martyr, First Apology, 66 (c. A.D. 110
-165).
Infant Baptism
“For He came to save all through means of Himself—all, I say, who through Him are born again to God—infants, and children, and boys, and youths, and old men.” Irenaeus, Against Heresies, 2,22:4 (A.D. 180).
Mary-Mother Of God
To all generations they [the prophets] have pictured forth the grandest subjects for contemplation and for action. Thus, too, they preached of the advent of God in the flesh to the world, His advent by the spotless and God-bearing(theotokos) Mary in the way of birth and growth, and the manner of His life andconversation with men, and His manifestation by baptism, and the new birth that was to be to all men, and the regeneration by the laver [of baptism]. St. Hippolytus -Discourse on the End of the World, 1 (AD 217)
Veneration of the Saints
“[T]hat it is neither possible for us ever to forsake Christ, who suffered for the salvation of such as shall be saved throughout the whole world (the blameless one for sinners), nor to worship any other. For Him indeed, as being the Son of God, we adore; but the martyrs, as disciples and followers of the Lord, we worthily love on account of their extraordinary affection towards their own King and Master, of whom may we also be made companions and fellow disciples! The centurion then, seeing the strife excited by the Jews, placed the body in the midst of the fire, and consumed it. Accordingly, we afterwards took up his bones, as being more precious than the most exquisite jewels, and more purified than gold, and deposited them in a fitting place, whither, being gathered together, as opportunity is allowed us, with joy and rejoicing, the Lord shall grant us to celebrate the anniversary of his martyrdom, both in memory of those who have already finished their course, and for the exercising and preparation of those yet to walk in their steps.” Martyrdom of Polycarp 17,18 (A.D. 157).
Mary Immaculate
“He was the ark formed of incorruptible wood. For by this is signified that His tabernacle was exempt from putridity and corruption.” Hippolytus, Orations Inillud, Dominus pascit me (ante A.D. 235).
“This Virgin Mother of the Only-begotten of God, is called Mary, worthy of God, immaculate of the immaculate, one of the one.” Origen, Homily 1(A.D. 244).
There was no "Catholic Church", there was no unanimity of thought, there was no such thing as a Papacy prior to Constantine. Constantine chose the "winner" and provided the protection and patronage for the establishment of the "Catholic Church".