Yes, it is: the Trinity and homoousios summarizes what scripture says. Transubstantiation takes what scripture says and hammers it into a foreign worldview.
Transubstantiation makes the error of trying to explain what the scripture does not.
I think they are the inevitable result of an arrogance in Rome that brooked no dissension: arrogance leads to arrogance, so every church leader from Zwingli and others onward decided they could found their own churches.
There are many reasons why churches have split or new ones established. Because of the diversity of the reasons, any simple claim or condemnation is necessarily incomplete or misleading.
Instead of listing the diversity of reasons, I would like to point that having common administration/organization is not a necessary condition for unity. Two churches may feel that they are parts of the same universal body of Christ and cooperate even if they are not officially parts of the same organization. It may even be easier to cooperate at the practical level when disagreements about doctrinal details or leadership do not clash - all cooperating churches may keep their own peculiarities and the others do not need to play the role of the guardian of correct() doctrines.
Belonging to the same organization was not a condition of unity in the earliest church network, so why should we put all Christians into the same organization to fight for the differing interpretations and leadership?
It would not work, unless one strong player takes the role of a dictator and forces everybody else to submit despite disagreements. Such power in the hands of one person corrupts and if the power is close to absolute dictatorship, then it absolutely corrupts. Without dictatorial authority, the forced apparent unity fails and the organization is doomed to split.
There is nothing wrong with explaining what scripture does not. But I am careful to distinguish transubstantiation from the early Church’s universal believe in the literal flesh and blood of Jesus. I accept it on the basis of being Catholic in addition to it being entirely congruous with what Jesus and the early Church taught and believed about it. If someone wants to just call it a divine mystery (it’s the flesh and blood Jesus but I don’t understand how, so be it. Granted it is a miracle, it is a divine mystery to Catholics as well in a sense.
It’s a combination of both. Without the Magisterium to interpret Scripture, interpretation inherently decentralizes. Then you end up in a Biologos thread where fourteen different Christians argue fourteen different positions on an issue. The Church did not handle Luther properly and parts were mired in sin and turned “My Father’s house into a den of thieves.” Jesus would have been overturning pews.