I'm talking about the theological paradigm of AM, as it relates to itself. That is, the implication that Judiasm, Christianity, and Islam are all ultametly correct doesn't work (ie, it's internally inconsistent), unless you have some form of "many paths to the Divine" idea, which in turn I pulled from Hinduism. Which doesn't show up too much in any of the three (there's a bit of it in...one of the letters of Paul, I think, remarking about how to get along with people whose theology isn't exactally the same as yours).
Regardless, my comment is that, as the youngest of the three, Islam is forced to deal with the existence of the previous two religions in its core scriptures, and as such ends up creating at least a baseline theological framework for partial inclusion.
However, more generally, I'm talking about a fictional game-world which explicitly takes a "what if..." and runs with it. In partiuclar, "what if the myths and legends of mideval Europe were substantively true?" As a consequence, that includes "what if the abrahamic religions were substantively correct?"
So, to answer your question: yes. For the purposes of Ars Magica (a fictional game world developed by Atlas Games), "Abrahamicism is the only truth". You have summed it up well. Add on "...as understood by mideval Europeans, with the inclusion of regional myth and folklore", and you've pretty much got the game world.
That's kind of the point.
If you don't want to play that? That's fine. It's not like the Game Police will come down and take your sourcebooks away from you. You want to change the RAW? Other posters have given you the simple rules solution (play around a bit with the Dominion numbers, or just declare the Divine to be a particulary powerful form of monotheistic farie-dom).
I've found that games that do this tend to loose flavor for their universality. That is, finding a core game mechanic that allows you to cover all cultural instances of religion and magic tend to come across as bland, IMO. Mage: the Ascension (2nd edition) probably the best example I've seen at this, although Witchcraft also get hit with this, IMO. (Note that I haven't been involved in the RPG scene since the mid 2000's, so my info is up to a decade out of date.)
Because, really - what it sounds like you were looking for is Mage, rather than AM. (Even Mage: Sorcerer's Crusade, which is set 300 years after AM is set.) Which is fine - I've got an entire shelf of Mage books. But the compromises that system makes in order to be universal means that the game mechanics tend to stick out in-game a bit more. (ie, it's obvious to most of my characters in-game that every other magic user is using the same metaphysical rules.)
At least in AM, there's an in-game reason for why everyone in the order talks about the game-mechanics as though they were phyiscs: it's written that way, with a tight coupling of game-world to game mecanic. That's a feature, rather than a bug.
And just off the top of my head: games that don't use Europe or Christianity as their base metaphysic (again, with the understanding that my gaming shelf is a decade out of date):
- D&D - a complete cludge of 1970's pop fantasy tropes (Lord of the Rings, Elric, Dying Earth, Farfd&Grey Mouser, high school mythology), but the underlying default religon is basically generic panthiesm with zorastrianism thrown in.
- GURPS and HERO - both of which are universal systems, and as such you can pick which sourcebook you're using to build your world with.
- Exalted - Greek with Chinese/Asian (and Cthulu) mythology and an anime vibe thrown on top.
- Old WoD - all of them but Vampire: the Masquerade. Mage = almost complete religous subjectivism, Werewolf = mix of various anamist religions, Wraith = exisistentilist greek underworld, and Changeling = metaphor for growing up. (They all had "the world is about to end", but that's hardly unique to monothiesm.) I have no idea about the new version.
- Star Trek, Trinity, Blue Planet - all sci fi, and definately not based on Christianity. (Counterexample: Fading Suns, with is pretty much "mideval European society in space")
- Legend of the 5 Rings, Sengoku - explicitly set in historical asian society, or else inspired by Asin myth.
- Big Eyes, Small Mouth - any of their games that are based off of Japanese anime are, well, based off of Japanese anime.
- Call of Cthulu - mystic athiesm, essentially (the horror of realizing humanitity's true insignificance to an uncaring universe).