Honestly, I dont want to sounds like a jerk, but those are... byzantine details. Jesus never cared about details much, as long you followed his teaching of love and good heartedness.
So yes, in a way, its silly. god dont care if you think he is one or many, I bet, at the end.
You don't
sound like a jerk, you
are a jerk. Okay, we get it, you're an atheist, you don't like religion. That doesn't give you a right to be a prick and give your two-cents.
Speaking as an agnostic student of Byzantine history and its theological disputes:
To them, whether Jesus was GodandMan or Man or God is over something both fundamentally important and about things that make a big difference in His nature.
To pick an example of something that looks ridiculously abstract, but was treated as extremely serious business because it is extremely serious business if you believe in that stuff at all.
Or take crossing yourself. Doing it improperly is not merely using the wrong fork at the table, its the difference between Godly and Ungodly.
The question is not whether or not they were hard headed. To look at it like that is to miss why it was so important that they be right on these issues.
Telling them (on either side) that it was a dispute over incredibly minor issues would be like explaining to a scientist that the disputes over Intelligent Design or Young Earth is "over incredibly minor issues".
To pick something that might give a sense of the weight of these things, though obviously only partially so - the fate of our immortal souls is not dependent on whether Terra is billions of years old or thousands of yeas old.
You missed the point completely and could not have possibly chosen any less-important issues save for maybe the colour of the clergy's vestments. And both Churches believe in evolution and that the world is four-billion years old; I don't know where that came from. How to make the sign of the cross isn't anything either side cares about. I'm talking about
*Original Sin- they believe that we're at fault for Adam and Eve's problems and humanity is naturally sinful, we believe that it's not our fault and we just inherited spiritual sickness and a fallen world.
*The Divinity or Humanity of Mary- they believe that Mary was born without sin, we believe that she was a regular person like you and I.
*Purgatory: They believe that there is a state that is either Heaven nor Hell that a soul goes to after death. We believe that Jesus Christ died for our sins and ask why would there be another trial after death preventing us from going to Heaven.
*They're also a lot more legalistic; whether you took confession twenty years ago and then you died or whether you took confession the day before you died matters.
So do you both want to argue with me about the differences between Eastern and Western Christianity? I've got a few more major differences, I can do this all day if you both want. I didn't even touch on the topic of Rome's-primacy; I could write you a short essay on that topic.