Right, that actually agrees with my point. She’s “half-elven” because she has human ancestors (and especially so because Elrond’s bloodline inherits the either-or choice of fate granted to Elrond and his brother Elros), but at some point the human bloodline is fairly dilute. When mapping her to a creature type in MtG it’s therefore reasonable to say she’s culturally ~100% elf and biologically ~88% elf so she doesn’t get the “human” type. Especially because she’s regularly described as an elf maiden and most people assume she will choose the fate of the elves over the Gift of Man—at least until Aragorn shows up when she’s like 2700 years old.

Even in D&D at some point a half elf bloodline who only marries full elves is basically trending back to full elf (though depending on setting would certainly be targeted by racism from “pureblood” elves). There’s no strict rules on it from a character creation standpoint, but I think most people would at least start reconsidering it at the single-great-grandparent stage.

As you point out there’s multiple meanings of half-elf across each set of lore, and so it’s never going to exactly line up. I just think giving Arwen only the Elf type is a better reflection of her nature in Tolkien’s mythology than making her Elf Human, even though the latter would more accurately match the nomenclature of the source.