Where in this is the Christian God?
Eru is God. The Ainur are the angels. Melkor is Lucifer. And as mentioned prior, the Holy Trinity is generally acknowledged as existent in-verse (The Flame Imperishable, which resides in Eru as that which ensouls and enlivens beings, is explicitly the Holy Spirit. Later writings mention that Eru will one day incarnate in human form, too). It's supposed to be Tolkien's own Catholic faith seen through the lens of a prehistoric mythic civilization, without making the conventional view of the figures nonexistent in-verse (Since the modern times exist in Tolkien's Legendarium, too)
The rough outline can be based on these two reasonings: accuracy and intention.
When I say intention, for example, Dante wanted to add his Christian religious views of God from the Bible into his story from what I've seen on the internet, and it has the visual accuracy with barely any differences that would suggest that it is something else that's not from the religion in real life.
Unless I'm missing something else, this would ensure us if it's putting real world religion in one's fiction or not
Yeah, that is precisely what I am concerned with, since, as said prior, this has the potential to mutilate quite a bit of verses if applied. Furthermore, there is also the question of exactly which part we don't want the verse to be "accurate" to. Would a verse acknowledging God as the Holy Trinity mean its "God" character is now disqualified from being indexable, for instance? What aspect of the IRL figure is a verse not allowed to cover without getting the axe?
Of course, given the primary concern here is "It's the same thing as tiering the actual religion!", I'll rip off the band-aid and cut down to the logical conclusion of that line of thinking: What we wouldn't want the verse to be accurate to is the metaphysics underpinning the tier of the God character. This leaves us with an interesting scenario: Religion and theology are linked to the metaphysics, but the metaphysics themselves are wholly separable from religion and theology, which means that those same attributes that make the fictional "God" a certain tier can also be found in characters that have little to do with actual religion.
An example that I often like to use is probably the following: It is affirmed by any classical theist that God is above space, and furthermore that God is above time. These are the attributes of Immensity and Eternity. Obviously, though, in fiction you will find
a great deal of characters who are above space and time. Are we to just, refuse to tier these characters, then? Under the accusation that, when we do so, we are technically tiering an attribute of God.
An objection that may be raised is "These attributes are fine to be tiered when they're attached to characters who don't correspond to any particular religious figure." Yet the cries of controversy largely boil down to "This will upset people," as Grath pointed out up there. So even if the character is not "Religious figure + Metaphysical attribute," but instead is "Wholly fictional being + Metaphysical attribute," it could still be called problematic, insofar as people can feasibly just make the connection in their heads and complain anyway.
So, as far as I see, this whole line of thinking leads to a pretty slippery slope where we just... refuse to tier or index any metaphysical thing whatsoever, because all metaphysics has been incorporated into some religion, in some way, shape or form. And frankly this is just an utter mutilation of the wiki.
And when I say "refuse to tier," I don't actually mean "Refuse to tier it highly," mind you, but refusing to even
index it in the first place, since "Well, let's tier it differently" would just lead to arguably much worse scenarios. For instance, in the old Tiering System that recently got replaced, Dante's God would have been...
Low 1-C, which manages to be objectively even more offensive than the sandbox that people are already finding disrespectful.