What? How is that in the core Christian theology. The core of Christian theology is belief that Jesus died for the sins of humanity. That is also a matter on which I think someone could be judged not-a-Christian even if they were to claim that they were. People can make all sorts of ridiculous claims. But no, the day and time of his crucifixion are trivial pursuit questions.
You're judging them as trivial. I think the rest of us kinda disagree. The time and manner of Christ's death is very important to the theology of his supposed demise and thus the theological implications inherent therein.
But there are other, even more critical contradictions there. Such as his final words. Was his final cry "My god my god why have thou forsaken me?" or did he utter "It is finished"? The theological implications of each phrase uttered is actually critical to the question of his divinity. If he cried "My god! My god! Why have you forsaken me?" this implied that he was a mortal man, possibly even a deluded fool, and certainly a man involved in a situation far beyond his capacity to control. This is why by the book of John he is declaring "It is finished!" a command, a dictation that demonstrates he has authority over the situation, and he is laying his life down willingly to accomplish the task his father has given him.
The theological implications
from an internal perspective are incredibly important.
No. Rites of succession for caliph are not a "foundational" belief in Islam like say believing that Mohammed was the last prophet of allah. That would also, I think, represent a valid dividing line.
But again, from the internal perspective, Muslims profoundly disagree, to the point they've waged wars over that foundational distinction, and have had goals of eradicting the other viewpoint as heretical and thus against Allah's will.
I think no matter what comparison made, you'll attempt to simply write it off by fiat because it is inconvenient to your position, not because they are in any way not viable models of comparison. They all very much so are.
No offense but you're really seriously starting backwards here. You're trying to use what needs to be your conclusion (your view of what communism is) as a premise.
How so?
Yes or no: are there any people who aren't Scotsmen?
There may or may not be, but so long as all the people we are discussing are self defining themselves that way, and are presenting themselves that way for the most part, and generally seem to share mostly similar views, etc. I have no justification for excluding them from that subset.