That has NEVER been taught by the Catholic Church. It is not Catholic. The Orthodox reject the office of the pope the same as Luther. They are schismatics and heretics. You said that Catholics like the writer of this thread's article, SSPX, and sedevacantes, are not sbeing submissive to the pope, like Luther. And yet, now, you say that the Eastern Orthodox, who reject the office of the pope, are part of the Church.
You strained a gnat and swallowed a camel.
You are aware that we are in communion with the Orthodox? Have always been.
They do not extend the same grace. The issues with the Orthodox go all the way back to the Great Schism.
Their argument is not that they are outside of the body, or that the current pope is illegitimate. They argue that the 5 are 2.
I don’t believe the history supports their argument, which is why I’m not Orthodoxy, but they are not arguing that Benedict XVI is not the legitimate pope.