I did actually address the thread. The article made statements about the Catholic church and I refuted them.
Constantine's own words confirm the allegations in the OP. Let's have a look at what he has to say (again):
Let's review:
Unam Sanctam:
“Furthermore, we declare, we proclaim, we define that it is absolutely necessary for salvation that every human creature be subject to the Roman Pontiff.”
Constantine’s position on his relationship with humanity:
and since it seems to me a very serious thing that in those provinces which Divine Providence has freely entrusted to my devotedness,
but also against me myself, to whose care, by His heavenly Decree, He has entrusted the direction of all human affairs
I myself, then, was the instrument whose services He chose, and esteemed suited for the accomplishment of his will.
Believing, therefore, that this most excellent service had been confided to me as a special gift, I proceeded as far as the regions of the East, which, being under the pressure of severer calamities, seemed to demand still more effectual remedies at my hands.
I have written to them under divine direction. (I though only the pope/magisterium could operate under divine direction?)
through the power of Almighty God, and at the same time the counsel and aid which he is pleased on many occasions to administer through our agency;
Constantine considering himself numbered amongst the bishops:
I call on Divine Providence to assist me in the task, while I interrupt your dissension in the character of a minister of peace.
at which I myself was present, as one among yourselves
I assembled at the city of Nicaea most of the bishops; with whom I myself also, who am but one of you,
Constantine determining the form and format of worship:
I shall render it most clear to all, both to Caecilian, and to those who are acting against him, by reading a perfectly plain judgement, as to what and what kind of worship is to be given to the Supreme God, and with what manner of service He is pleased.
What can be done by me more in accordance with my constant practice, and the very office of a Prince, than, after having driven away errors and destroyed all rash opinions, to bring it about that all men should show forth true religion and simplicity in concord, and to render to Almighty God the worship which is His due? (Is not one of the pope’s titles Successor to the Prince of the Apostles? Peter did not consider himself a prince, but a servant.)
My design then was, first, to bring the diverse judgments formed by all nations respecting the Deity to a condition, as it were, of settled uniformity;
Permit me, who am his servant, to bring my task to a successful issue, under the direction of his Providence, that I may be enabled, through my exhortations, and diligence, and earnest admonition, to recall his people to communion and fellowship.
I shall also make these persons see what worship and what kind of worship is to be given to the Divinity,
I shall endeavor with all my power to cause that what is contained in the Divine Law may be preserved inviolate,
Shouldn’t the pope determine what kind of worship should be given to God, in concert with the Magisterium?
Constantine rendering judgements upon the clergy:
Those same persons who now stir up the people in such a war as to bring it about that the supreme God is not worshipped with the veneration that is His due, I shall destroy and dash in pieces.
I shall without any delay cause those men whom I shall ascertain to have acted against that which is right and against religion itself, and whom I shall discover to have been guilty of violence in their worship, to undergo the destruction which they have deserved by their madness and reckless obstinacy.
since I am going most diligently to search into the things which concern not merely the people, but also those clerics who are in the first places, and shall pass judgement in accordance with that which is most clearly in the interests of truth and religion.
I will immediately send some one who shall depose you by my command, and shall remove you from your place.
I formerly gave command that certain bishops should be sent from Gaul, and that the opposing parties who were contending persistently and incessantly with each other
I guess we could call these miscellaneous pope-y statements:
For I was aware that, if I should succeed in establishing, according to my hopes, a common harmony of sentiment among all the servants of God,
I have judged that it ought to be the first object of my endeavors, that unity of faith, sincerity of love, and community of feeling in regard to the worship of Almighty God
I beseech you, therefore, in post haste, as the phrase goes, to assemble together, without any delay, in formal synod; so that you may support those who require your assistance.
Nothing shall be omitted on my part to further the interests of our religion. I have done all that you recommended in your letters.
I have sent to those bishops whom you specified, directing them to repair to the council for the purpose of deliberating with you upon ecclesiastical matters.
whom I have commanded to hasten to Rome for this purpose, he may be heard, as you may understand to be in accordance with the most holy law.
Nevertheless it is expedient that your Prudences should be made acquainted with my opinion also.
The OP contends that the RCC is nothing more than warmed-over Roman paganism. The claim is backed up with quotes from Constantine himself. The RCC claims it was divinely instituted by Jesus. Refuting the OP should be easy; no interpretation of scripture is required for this. All you would have to do is provide letters from the Bishop of Rome, addressed to the universal church, from prior to circa 313 A.D. that uses the same type of language as that written by the Pontifex Maximus of the Roman religion, Constantine. There has to be a papal bull or something lying around, no?