Thank you, Soldier.
You will find, if you deal with them again, that the EO are the original Protestants. The modus operandi is pretty typical, as has played out in this thread. They will bomb with obscure historical "facts" and try to appear of superior knowledge as pride and non serviam are their denominational traits. Most Catholics know nothing of the Donation of Constantine because no Catholic doctrine depends on it, as Bp. Sanborn already told LeDeg. It is a classic straw man argument. It has no bearing on the spiritual authority of Peter. They will ignore all other references, citations, historical evidence, and straw man this topic and other forgeries to death, claiming that these are the ONLY basis of papal supremacy or the filioque, or x, y, and z. They count on not being fact checked. But when challenged to show where the excommunication of Cerularius rests on the Donation, it's not there. They can't. Same with St. Thomas and "Against the Greeks" or Vatican I. He claims Vatican I relies on a forgery, when right in the Council itself, it quotes the Council of Ephesus (431) verbatim! Even if St. Thomas referenced a forgery (something real historians debate), anyone with basic logic skills can see that his arguments stand without those. And all it takes to disprove the claim that a forgery is the basis is ONE of the myriads of docuмents that exist from the very early Church from their own Eastern fathers clearly writing to the popes as superiors, or the pope acting as such. But still, they don't get to say "X doctrine is based on a forgery" simply because the forgery also contains the doctrine. If anything, the fact that the forgery was accepted at all is more proof that the doctrine was universally held prior to that, as if it introduced a novel doctrine, it would have come under more universal immediate scrutiny.
LeDeg has made his public apostasy here, years ago. He refuses to believe what the Church teaches or do his own research, but continues going to anti-Catholic sources that feed his pre-existing bias. When he is called out on his copying and pasting and pseudo-research, as I did last year, he goes back to building his trad street cred in the Jew threads, but still pops in with his little seeds of doubt to plant in the minds of others. I hope that some of those who have disappeared from here were not swayed by him and his assistants. But the EO have really zeroed in on trads as prime for the picking because trads are troubled, and rightly so, by the length that this crisis has played out and the confusion. The EO prey on it, but offer no real solution because, if anything, the EO are in far more disarray than the Church of Rome.
One other resource you may want to check out is the Resistance Podcasts series with Dr. Alan Fimister on the Councils. Most Catholics have not really studied these, but a good knowledge of the Councils will help one to grow in the love of the Faith as well as to deal with the attacks from the outside.
A trend I have noticed, and I would be curious if you find the same, is that the EO arguments changed post-Reformation and they started borrowing heavily from the Anglicans.