So why did Honor wonder whether the loss of access to Dawnshards was so significant to this conflict?

[Ripheus23]

To my knowledge, we have it confirmed that Hoid, holding a Dawnshard, therefore has held a Dawnshard in the Rosharan system at some time. If he came with the refugees from Ashyn, I assume he had it then too. If he mediated Odium's early interactions with the humans of Ashyn, and if he had a Dawnshard, and a combination of Odium's influence and Dawnshard levels of power is what brought ruin to Ashyn, do we imagine that somehow using Hoid's "Exist" Dawnshard would be liable to causing that kind of effect?

Elsewhere/wise, we see the Change Dawnshard on Roshar. From the theology of Ruin, we know how the Intent of Change can coincide greatly with the will-to-destruction. So, I could more easily try to predict that it was the Change Dawnshard that was the primary relevant type of culprit in the desolation of Ashyn. (Or: why would the Sleepless worry about the carrier of Change? Undoubtedly, they as a secret society are interested in Hoid; but worried about him when he has/had a Dawnshard? I don't know...)

But, isn't it always written that the Dawnshards, plural, contributed to Ashyn's fall? Now if Change can be so dangerous, then Change and Exist could be too, I should guess. In formal logic they say that if it's a fact that A, and A implies B, then if some random other C is true on its own, then (A & C) also implies B. It's called monotonicity or something. So, it's not a difficult exercise in abstract representation to subsume, "Dawnshards, plural, devastated Ashyn," under, "Change primarily, modulated by the otherwise less menacing powers of Exist, did that thing."

One of the following statements is not a theory or prediction. It's not even supposed to be a guess. It's more like a thought experiment, following the internal, rigorous logic of magic in the cosmere. So: it's generally possible that three or all four Dawnshards were involved in what happened on Ashyn. However, if using all four, perhaps alongside implements like the First Gem or whatever, could destroy the most powerful physical entity in the cosmere's known history, how could Ashyn have not been utterly atomized (axified!) instead, then? So, I would like to think that not all four Dawnshards were involved with what happened on Ashyn as such.

On the other hand, it's rather surprising that the Change Dawnshard would be in the Rosharan system specifically, that Hoid would not only go to Ashyn and meddle, but then transfer to Roshar and meddle some more, holding another one. These are the kinds of powers that Ruined Adonalsium, yet the Shards, in their epigraphic letters, don't seem to be worried about anyone or anything having them on Roshar. Like, okay, you might not think Rayse to be all too bad, maybe like Endowment you think that e.g. Ambition was equally or more menacing, no less. Okay. But Odium was in the proximity of at least two Dawnshards, one of the bearers of which he gained horribly direct powers over the mind and body of at various inopportune moments. From Hoid's reaction to Retribution's manifestation, it seems like he feared that the Exist Dawnshard could fall into some kind of enemy hands. In context, that would probably be his Rosharan enemy par excellence, it's not like we see farsighted Ghostbloods or Scadrians or whoever popping up at the moment Hoid is vaporized and trying to grab the Dawnshard. So, it will have always been that Odium getting the Exist Dawnshard would be an unwelcome development, and nothing much suggests that Rayse would've been overwhelmingly averse to holding a Dawnshard. (Granted, he would still have not wished that his Intent, as Odium, would Change, so that e.g. the Change Dawnshard might specifically not appeal to him. But the Exist one? To exist generally doesn't seem incompatible with retaining the profile of divine hatred.)

Moreover, Rayse would've been willing to do something with the power of the Dawnshards, being one of the sixteen who directly or indirectly used them to kill Adonalsium. And then however he influenced the Ashynites, well...

So, again: and the rest of the Shards really were just like, "So what?" (Okay, maybe not Harmony, or not other ones we've not seen letters from.)

All that being said, it seems like there could be a third Dawnshard in the Rosharan system. This is a guess: perhaps that's what, "Unite them," is about, something left behind by the power of Adonalsium that would reach towards the reunification of the Shards. Maybe from Adonalsium's point of view, being killed and having its power redistributed was at best a temporary dynamic that would inevitably be recouped by reunification. Who knows (besides Sanderson, if he's settled on a canonical final outcome yet), but (A) Honor was worried that the Knights Radiant/Rosharan Surgebinders would be themselves the true desolation of Roshar, as had occurred on Ashyn, except (B) the Rosharans were later bound by oaths to limit their powers (this was the point of their relationship with Honor's power!), and had not the Dawnshards.

Or did they?

If holding a Dawnshard has a special impact on one's Spiritweb, I daresay it seems plausible that Nohadon held one, that this accounts for his especial presence in some of the visions. However, I haven't yet found a way to reconcile, "Honor was worried that Rosharan Surgebinders would destroy Roshar," and, "Honor knew the Dawnshards were necessary for that," alongside, "And Honor blessed the Knights Radiant for their oaths," but, "It was in Nohadon's time that the oaths were first sworn," and yet, "There were Surgebinders before the Knights Radiant." We are not shown (to my memory/knowledge) anything about whether Rosharan Surgebinders retained Dawnshards during or after the voyage from Ashyn, etc. How were Rosharans Surgebinding without swearing the oaths that entangled them so magically with the mindful spren? Why were Honor and Cultivation allowing this?

If humans had lost access to the dangerous Dawnshards at that time (even whenever Hoid was focused and present on Roshar), then why would Honor be so worried? Yet then in the present time, why would he worry about the loss of the Dawnshards and their dangerous powers? I don't get it...