A note about
@ThoughtfulSaint's latest series of videos on how the Trinity makes no sense. They are good videos, and I recommend you watch them, but as the resident Trinity whisperer I thought I should chime in.
I teach art history, and I always tell my students, if you want to understand an art movement, you should study biography, not theory. It matters a lot more that the Fauvists were all students of Moreau, than anything they later say about their art. Once you know that, the pieces start to fall into place.
In the same way, you can't understand the Trinity without understanding the history of how it came to be.
You have to understand that they thought the divinity of Christ was under attack by various forms of subordinatists, who wanted to demote Jesus to a demigod or man chosen God. That's the ballgame in their view. That's the end of Christianity and the whole concept of an infinite atonement and the promise of eternal life.
Years ago, when I was a mission leader, I presented this option to my missionaries, you have a choice between a Christ that is less than divine, but separate, and one that is divine but is the same essence with the Father. Which do you choose if there are not other options? After some apprehension, they chose the latter. Any sane person would do the same. It's the only one that preserves an infinite atonement. (This presents an interesting tangent for Reform/Calvinists who don't believe in the infinite atonement, but let's leave that alone for the moment.)
The proponents of the homoousian trinity saw it exactly as just such a stark dichotomy. Not everyone agreed of course, and many didn't see it nearly so cut and dry, and most of the empire remained "quasi-Arian" (a problematic and inaccurate term but we are stuck with it) for many decades after Nicaea. It took nearly 60 years for the homousian trinitarians to convince people otherwise, and Athanasius spent most of his life in exile, but that's another story.
I think the fact that the second we challenge the homousian Trininty people automatically accuse us of being subordinatists who reject the full divinity of Christ (for the record, we do not) shows how strongly this dichotomy is engrained into the debate. I also think it helps LDS understand why the homoousian trininty is so ardently defended. From their perspective, we are saying Christ can not perform the atonement because he is not fully God.
In the most charitable terms, the homousian Trinity is the nuclear option. It is a maximalist argument which makes even the most remote attack on the divinity and subordination of Christ impossible. That's why it got endorsed and codified. Its strength is found in its surety against a particular attack against Christ's divinity. It is an overcorrection that, in our opinion, just misses the mark and goes beyond Biblical teaching.
Before we make any headway in interfaith dialogue we have to understand that is why they defend it so much. We have to see it how they see it before we can even begin to argue for a third way. We have to present the history of how the homousian Trinity came about, to explain that it was mostly crafted by dialecticians out of a particular fear of the 4th C, than a reflection of actual biblical beliefs and traditions in the first centuries of Christianity.
The value of dialecticism in a theological debate, well, that's a whole other issue, but we can start here.
Hope this helps.