>but that doesn’t make it an exclusive biosignature. There are plausible abiotic pathways for DMS formation, such as in geochemistry we can’t know entirely about because we live on earth.
I'm sorry, but this is ridiculous. You started by acknowledging that it is indeed exciting, that it is something we only understand to be produced by living organisms. I wholeheartedly agree with that. And so the plausibility of an abiotic alternative is the big question.
You suggest that there are plausible abiotic pathways, but I think that's where this all starts to go off the rails, because I don't think there are in fact plausible abiotic pathways. We absolutely should attempt to model such possibilities and should be extremely careful about assumptions before working that out. But the state of our knowledge thus far counts for something too and it would suggest that such a process is pretty rare or unique. And then it really goes off the rails because instead of an actual example, you suggest not any specific known pathway, but a kind of bizarre philosophical musing that maybe there's "geochemistry we can't entirely know about."
We most definitely are capable of modeling chemical processes even if they don't happen on Earth. And there sure as heck is no such thing as a principle that things beyond Earth's surface are things we "can't" know about. I truly can't stress enough how ridiculous an assumption like that is.
We know, for instance, that gas giants are capable of producing phosphine, even though that doesn't happen on Earth. We know that the moon likely has a molten core. We know all kinds of things about atmospheric chemistry of planets and stars, because even if the abiotic processes can't be witnessed directly on Earth, we know enough about the principles of chemistry to model them in new contexts with reasonably high confidence.
And that's before we get to the idea that such uncertainty about off-world chemistry can be treated as tantamount to evidence of known abiotic process. It's nothing of the sort, it's more like "who knows, maybe it's possible." We do indeed have to figure out if there are such things as an aviotic process, but just the idea that, hey, who knows, something offworld might be happening is nowhere near enough to count.