Why did the Orthodox and Catholic churches really split?

Apostolic succession versus papal authority is part of the equation, but it isn't the totality of it. A big part that gets missed is the Filioque, the modification of the Nicene Creed. The problem with the modification is this: if the creed needs to be modified, then it wasn't inspired by the Holy Spirit when it was revealed to the church. The understanding of the Orthodox Church is that everything that comes out of the councils is inspired by the Holy Spirit, in the same way that those who wrote the holy scriptures were inspired by the Holy Spirit.

So if you have to go back and change the councils, you're not going against the church, you're going against the Holy Spirit. That is one aspect. The second: saying we're just arguing over papal authority is reductionistic. We agree there was a first among equals. But there were whole councils where the See of Peter didn't even show up. There is no historical witness that testifies to that kind of supremacy.

And if papal supremacy were the most normal and natural thing, why was there a Great Schism? Why did it take a thousand years for everyone in the East to not understand that this was what was going on? It became a great schism because it was a complete deviation and mutilation of the teaching of the church fathers, which is that Jesus Christ is the head of the church.