Here, in
Coda, the Devidians seem like a
really small-scale, localized threat to the the universe as a whole. There are galaxies on the far side of
Laniakea that are getting snuffed out because of the Devidians. When you stop to contemplate the scale of the universe, it's just as likely that something on the far side of Laniakea, or even one of the more distant superclusters, places little more than bare pinpricks of light from our vantage point, could collapse the universe -- and our 24th-century heroes would be completely powerless to stop it and would never, ever know.
That's why I'm not fond of stories about things that could destroy the entire universe. Given the effectively infinite size of the universe and its immense age, if there were anything that could destroy the entire universe, then surely it would have already happened long, long ago.
But there's something I pointed out in
DTI: Watching the Clock -- despite how we talk about them, parallel timelines do not encompass the entire universe. Quantum-mechanically speaking, when the observed universe diverges into two measurement histories, the divergence/superposition propagates outward as particles interact with each other, so it only spreads out at the rate of interaction -- which in real life means the speed of light at most. As far as anyone outside the light cone of that interaction is concerned, i.e. anyone far enough away not to have been affected by it, the split hasn't happened. So parallel timelines are more a local phenomenon than a universe-wide one. We only call them parallel "universes" because from our perspective as observers, they encompass the entirety of our experiential universe, i.e. the extent of what we can observe.
Granted, in Trek, there are all sorts of faster-than-light phenomena that can cause interactions to spread out far faster than they would in real life, like tachyons and subspace shock waves and so forth, which is how you can have, say, the Amargosa supernova having a near-instant effect on the courses of starships light-years away. So it wouldn't take long for a timeline divergence's effects to spread through all of known space or through a whole quadrant, or even the whole galaxy. But interactions between different galaxies are quite rare in the Trek universe, so other galaxies would probably be unaffected by any given timeline split within our galaxy, or by the collapse of any of our galaxy's distinct timelines.
From that perspective, it makes sense that a threat to the existence of entire timelines within our galaxy would have to originate within our galaxy. Although it's still a coincidence that it happened within the very tiny part of the galaxy that the 24th-century Federation has managed to explore.