(...the Catholic Church was never a part of the Orthodox Church, and thus never “left Orthodoxy”)
That depends on which version of history one is reading. Rome claims all of the other patriarchates left the Catholic Church. Our view is that Rome left the Church through her insensate, and often self serving, doctrinal innovations.
Your view is historically unfeasible -- a reason not least of which being that doctrinal innovations were far more prevalent in the east.
As a biased (Lutheran) third party, I often wonder if it was both sides leaving each other. By the time of 1054, the East spoke Greek, and didn’t speak much Latin. The West spoke poor Latin, and knew no Greek. Reading the notes from the councils translated into Latin and Greek, they read totally different (full disclosure, I don’t read Greek). At some point, neither side really understood what the other was saying. Or wanted to.
The East was worried about all the barbarian Germans running around with church titles, and the West was worried that the effeminate Greeks would demand they perfume themselves and bow before them. Both had an idea that church unity meant that they had to reside under the same Empire, which was going to be impossible by then.