But my question to you would be: what are the odds that our heroes are looking for a clue that will lead them to a Sith Artifact; and then they find a Sith Cultist, who has a mythical blade carved in ancient, unintelligible runes, and Rey can sense oodles of Dark Side energy coming from it.
The question is, what are the odds that this isn’t what they’re looking for? Balance of probability, and all of that. “Darn it, Rey, you were supposed to grab the other mythical Dark Side weapon that the Sith Cultist was hoarding in the cave that was emanating Dark Side energy! Doh!”
Like, seriously, how many Sith Artifacts do you think Ochi brought with him into this cave? They’re not exactly growing on trees, ya know? You said it yourself, 3PO is all about statistics. Statistically, how many magical Sith Artifacts are they expected to find?
EDIT: Okay, okay, okay, what if we could make 3PO say, “This must be the clue Master Luke was after”? Would that alleviate your concerns?
They’re not particularly looking for a Sith artifact, or a passage in ancient Sith runes, so the odds that it isn’t what they’re looking for are pretty high. Maybe Rey would think it’s important, specially if it calls to her, but unless the odds are 100% 3PO’s reaction to it would be off, and even if his lines could be altered seamlessly he would still be too cheerful over some meaningless runes. I think the best course would be to just let 3PO read the thing.