Except the problem with trying to account for an arbiter is that connection drags you straight into obsidian, and then she eats your face, and your juicy juicy data.
Where does the eat the face part come in? It's not like the Shard is going to connect or presumably mess with the link, assuming said Arbiter doesn't trigger. Unless we are going with the lines of thought that dimensional shenanigans, including other realities, somehow interacts with both the Flame and the brain of the Arbiter? As accounting for the Arbiter should be relatively easy, considering it is a singular person whose Shard-side model could be built up and expanded upon either via imperfect simulations/simulacrums, or simply observing the actions they undertake. So there's no actual need to really even hook up to their Brain or anything like that, but that is already out of the scope of PTV, in the sense, it can't directly control brains.
The fact that she's acausal and precog from Worm has no feats against that does not help.
In what way, considering that actual Time powers do exist in Worm, it is possible for acasual loops to occur and again it's not X Precog? Not to mention that there is limits on what Obsidion can do looking at the Information threadmarks. Besides, It would be PTV (of Zion, considering the prior context of possible fight) with an active Shard network of an incalculable but still finite size that is either actively in the field, or are being held in reserve, thus being usable, until a new Host is found.
Assuming that at a baseline they could detect the space-time warping of Obsidion's presence in the planet they'd at the very least have a definite target, and that the Data-absorption is limited to a singular spatial plane, ie not every single Earth in Worm, then the information it could pick on Shards would be limited to the connections of Parahumans. Which in of itself, is just burned-out hardware from the Shard that formulates the power expression from what I recall. That is further regulated and altered by the Shard touching upon what I assume are the finer details or software.
So the Shards, overall, should be able to detect the anomaly in Space-Time and by proxy Zion, given their nature, but it's uncertain what if anything Obsidion would pick beyond anomalies in physics around Parahumans or vaster Cycle shenanigans, like creating/finding alternate planes of reality where physical laws change, or are outright broken in some cases, such as Sting. Most Shards in a given Cycle are Supercomputers via a variety of mediums, and Obsidion could be said to be a Magical-Biological one, but I think the best comparison might be "
What if an Endbringer-like Being had effectively infinite power, to grow, change, develop, etc, and a wide capacity to gather information?" As I don't doubt that Obsidion is tough, but I don't think that they are Endbringer grade tough, akin to effectively (not literally) trying to get past a galaxy's worth of matter., doubly so due to the magic.
The major reason why I doubt that normally Obsidion would win, or is very unlikely to, against Zion (by itself) is that they operate on vastly different magnitudes, given one is a planetary parasite, and the other is a multi-versal parasite that is vastly larger to the point where Lavos is small. The former does have the advantage in figuring out how to have unlimited power, via magic that may or may not be copied/learned by the opposition, and more capable of abstraction though, and Zion is at it's weakest point, given it is not operating as an Entity but as an Avatar charged with protecting the status quo of the failing Cycle.
The hardest part about killing an Entity (assuming you're anywhere on their power-level) is that they're composed of TRILLIONS of Shards, and they're scattered across just as many universes. Even if a Lavos-spawn killed the Shard in the universe they're in, can they tell if, against all odds, that was one of the Shards that was important? Hell, can they actually attack Shards that aren't in the same universe as them? What's stopping the Entity from just firing Sting at it?
That's kinda like saying a human is made out of a trillion skin cells, equivalently, WOG-wise, and it gets even weirder considering that a Shard is made out of Shards, that can then be further split until there is a point where you can no longer say there are any Shards, as the identity of a Shard, and the Collective-Shardmass that is a Colony known as an Entity, is most of the time equal to their function and what best suits it, be it thought patterns, impulses, fallacies, and so on.
So I'd imagine a Shard's Soul would be something that both easily segments and connects with both each other and outside forces.
