Unless you’re referring to the novel, there was no indication in the film that the dagger was ancient.
I would have sworn the novel did, but that could be on me, actually. The text repeatedly refers to Ochi as a collector of “ancient Sith artefacts,” and I might have made that connection myself unintentionally. I’ll check.
If you ditch the compass in favor of Sith whispers or mystical guidance, you could use it to point to the Wayfinder regardless of where it might be. But you’d have to maybe have a sticky note on the handle he put the location onto.
The dagger really don’t make no sense.
My favourite part of TROS are the scenes with C-3PO; poor 3PO got really shafted by TFA and TLJ, and I genuinely love that he gets such a starring role in the first act of TROS. So as dumb as it is that there’s a map that points to another map like a videogame fetch quest, I do wanna keep the Sith translation as important as it is, so C-3PO’s sacrifice has the gravitas it should.
Plus, I don’t actually hate the Goonies-style “line up the dagger” thing as a concept. It is dumb that Rey just stands in an arbitrary spot anywhere on a kilometres-long shoreline for it to work, though, and my idea is to add a specific marker that she has to stand on and line the dagger up with, like the medallion in Raiders of the Lost Ark.
It certainly don’t make no sense, though, that’s for sure. I’ve spent longer thinking about it than Terrio or Abrams probably did.