Well, okay, so here's the thing. Let's pretend, for a minute, that Vorinism has some validity to it, and that there is a war for heaven.
If Shardblades kill the soul itself, wouldn't that kind of...I don't know...be like being balefired, the soul destroyed, unwoven from the afterlife, etc. etc.? I know nothing has been directly said, but there's a lot of attention paid to the fact the soul is actually cut by Shardblades, between the "eyes are the gateway to the soul," to the literal "it cuts the soul," I distinctly remember at least four or five times that point was made.
I think you might be onto something, something ingenious. Odium seems a lot like Ruin, but worse, and look how conniving Ruin was. He would give people power to manipulate them. Why wouldn't Odium, then, trick Honor and give men weapons that would prevent them from assisting Honor effectively.
I struggle seeing Honor creating blades that sever the soul.
The blades, in my mind, HAVE to relate back to Odium in some way. A guy running around splintering things left and right seems like the type to deliver a weapon that severs souls. Additionally, Syl's reaction rings in my head. I was 100% sure after this re-read I just finished yesterday that the blades have to relate to Odium. After all, Syl literally hisses when she hears Odium's name. Wouldn't she identify something of Odium as simply being "wrong?"
I mean, I know Sanderson is a very creative author, but let's compare Kaladin and Kelsier as characters for a minute. Both are incredibly powerful, natural leaders with a seething hatred for the aristocracy. They both have magical powers and are particularly gifted in combat, especially combat that involves manipulating their positioning as well as their natural strength. They also become "leaders" and develop religious followings (though not quite as potent with Kaladin, there's still plenty of usage of the word "devotion" regarding him). Even superficially, they do both start with the letter K and feature L and I.
Is it that unreasonable to then expect Sanderson to again employ a "blessing" that turns out to be a curse? Why wouldn't I expect Shardblades to work almost exactly like hemalurgy, except, worse, since it's Odium?
And lastly, I think the Knights gave up both the blade and plate because they were "quitting the game" so to speak.
Sorry for the slight tangent.