Here is an explanation of the classical Trinity that I can make sense of:
Similarly, in the Trinity, we have one nature–meaning one knowledge and one will–but three Persons possessing it. In our post-Kantian times, we would say that there are three “I”s in the Trinity and one in Jesus Christ.
I have a sense that the set of real theological and doctrinal differences between the churches and the set of perceived differences overlap, but maybe not a whole lot. Part of the problem is that when you take the best and most sophisticated version of a church’s doctrine, steelmanning it so to speak, it’s usually much closer to the best and most sophisticated versions of other church’s too. It’s pretty easy to see the peaks from a peak. Take deification, for instance. Even Catholicism approaches something like it when Catholic thinkers and mystics think seriously about when it means to be saved and communing with God. Only they hasten to add, there still is a basic ontological difference, blah, blah, blah. Mostly meaningless mumbo jumbo, as far as I can tell. As if one church were to say, we believe in this truth, and another church were to say, we also believe in that truth, but its totally different, because the truth we believe in now has more aether.
The problem is that religions don’t really function at the peaks. The wise and good versions of doctrines usually devolve into crude simplifications in the day to day life of the faith and as applied by the mass of the faithful. But one cannot just compare crude simplifications either, because how much and in what way a doctrine will be crudely simplified is unpredictable.