As a discussion topic I have also postulated the theory that the Latin Rite (or as I like to call it after it became such - the Frankish-Latin Rite) went like the "protestants" over the adoption of the filioque clause innovation.
As you wrote, Martin Luther was just a priest but had no authority to do as he did and introduce innovation outside of the council systen. My point is that the Pope, without calling a Church Council also adopted what the Orthodox still see as an innovation to the faith when he had no authority to do so. Being "First among Equals" does not grant any Pope the authority of an ecumenical council.
"It is a statement of opinion that one can argue (and it is juicy to argue) but not a basis for the hurtful words Kolokotronis used against the good father who used them in the article."
The priest's remarks were both ridiculous and ignorant, they are also not in accord with what his own hierarchs. Recently, the SCOBA bishops in consultation with a committee of the Catholics bishops issued a statement of the filique issue. In part it says, in a final section,that the Consultation makes eight recommendations to the members and bishops of the two churches. It recommends that they "enter into a new and earnest dialogue concerning the origin and person of the Holy Spirit." It also proposes that in the future both Catholics and Orthodox "refrain from labeling as heretical the traditions of the other side" on this subject, and that the theologians of both traditions make a clearer distinction between the divinity of the Spirit, and the manner of the Spirit’s origin, "which still awaits full and final ecumenical resolution." The text also urges theologians to distinguish, as far as possible, the theological issues concerning the origin of the Holy Spirit from ecclesiological issues, and suggests that attention be paid in the future to the status of councils of both our churches that took place after the seven ecumenical councils of the first millennium. And finally, in view of the fact that the Vatican has affirmed the "normative and irrevocable dogmatic value of the Creed of 381" in its original Greek version, the Consultation recommends that the Catholic Church use the same text (without the Filioque) "in making translations of that Creed for catechetical and liturgical use," and declare that the anathema pronounced by the Second Council of Lyons against those who deny that the Spirit proceeds eternally from the Father and the Son is no longer applicable.
This priest made his remarks after his own hierarch, a member of the SCOBA, endorsed this statement. To call Catholics "Protastants" is to call the heretics. That is innappropriate and the man should be disciplined. He is disobedient and if he preaches this garbage, especially to catechumens or new converts, he will be leading his parish astray.