There does seem to be a notable absence of any sort of "warspren," and this would be explained if every single Parshendi had bonded with a warspren, since lots of parshendi bonded with lots of warspren = strange absence of warspren. This would also explain the Parshendi's at first inexplicable assassination of King Gavilar, because it provoked a war, and it could also explain why they seem content to hang out on the plains fighting the Alethi without ever really trying to end the fighting or escape. It would also explain their weird sense of honor on the battlefield, since there usually is supposed to be "honor in war" or something like that, at least in medieval/fantasy settings there usually is. The way they grow armor stuff could be the type of surgebinding that is granted by bonding with a war spren. I would be interested to know if they already had the armor when Gavilar originally discovered them.
(What if there are still more surgebinding powers even beyond what the knights radiant used? Like, the knights radiant were bonded with a specific ten types of spren but a Nahel bond with any type of spren would produce at least some type of surgebinding.)
Since the Chasmfiends go into chrysalis, they have to become something, and Thunderclasts definitely seem the most likely candidates. However, one thing is: what about all the other Great Shells? Do they all become Thunderclasts? No way, although maybe there are more voidbringers we haven't been introduced to yet.
And, the Parshendi become chasmfiends become thunderclasts theory isn't directly contradicted by the low number of chasmfiends, as it could be like a "seed is planted, only grows into chasfiends sometimes" sort of things, and nor is it contradicted by them cutting open the chasmfiends because they could never hold the plateau long enough for the chasmfiend to completely change, and the parshendi would cut it open regardless, so they might as well cut it open to feed their army.
---perhaps the parshmen only become parshendi when they bond with warspren, although I have no idea how that would happen since the parshmen are so docile
That line about "his punishment demanded they didn't, his honor demanded they did," though, is very interesting. I hadn't even noticed it so thanks to whoever brought it up.